Finance calculator

Compound Interest Calculator

Work out future value and compound growth from a starting balance and regular monthly or annual contributions, then layer on compounding frequency, inflation, fees, and taxes to see the inflation-adjusted, after-cost result. Switch on goal planning to solve for the contribution, return, time, or starting amount a target needs. Charts, a year-by-year schedule, and a downloadable Excel model are included. Returns are estimates, not promises.

Estimate future value, interest earned, real purchasing power, and contribution growth in one clear calculator.

Best forSIP-style monthly investingSavings growthRetirement planningLong-term savings projectionsGoal planning
Updated June 2026No sign-in requiredEstimate only
Estimates only, not financial advice.

Compound growth planner

Build your compounding plan

Educational estimate only. Actual savings rates, investment returns, taxes, fees, inflation, and market outcomes can vary. Investment returns are not guaranteed.

Starting balance$10,000

The money you begin with today. Currency only changes formatting, not the math or any local tax rules.

$

Your current balance. Use 0 to start from scratch.

Used to label the schedule. Optional.

Regular contributions$500 monthly

Money you add on a schedule. Beginning-of-period contributions have slightly more time to compound than end-of-period ones.

$
Contribution timing
%

Raise contributions each year (e.g. with pay rises).

yrs

0 = contribute for the whole horizon.

$
Return and compounding7.00%, monthly, 10 yrs

Your assumed annual return and how often interest is added. Returns are assumptions, not promises.

7.00%

A long-run diversified stock-market average is often assumed around 6–8% before inflation — your account may differ.

Rate type

APY/EAR already includes compounding; a nominal rate depends on the compounding frequency you choose.

10 years

Time is the strongest force in compounding — later years often add the most.

Real-world adjustments3.00% inflation

Optional. Account for inflation, fees, and taxes to see a more realistic picture.

%

Used to show today's purchasing power.

%

Fund or platform fee as % of balance per year.

$
%

Simplified estimate; real tax rules vary by country and account.

Tax treatment
Round results
Goal plannerOff

Set a target and solve for what it takes to get there. Required figures are estimates, not recommendations.

Your compounding recipe
Starting balance
$10,000
Monthly contribution
$500
Annual rate
7.00%
Compounding
Monthly
Time horizon
10 years
Total contributions
$60,000
Estimated growth
$36,639
Estimated final balance
$106,639

What your compound interest result means

Moderate assumptionDescribes the 7.00% return you entered, not a prediction. Higher assumed returns carry more risk and are not guaranteed.
  • About 34% of your projected balance comes from growth and 66% from your own deposits. Growth becomes a bigger share the longer the money runs.
  • Inflation meaningfully reduces buying power: at 3.00% inflation, $106,639 is worth about $79,349 in today's money — roughly 26% less. Plan against the real value, not the headline figure.
  • Time is your strongest lever right now: one more year adds about $13,905, more than a 10% larger contribution would ($8,654).

These notes are generated from your inputs to help you read the result. They are not financial advice.

Why compounding accelerates

Early years

Your contributions do most of the work. In year 1, growth is only about 5% of the balance.

Middle years

Interest becomes visible. By the midpoint, interest-on-interest is a meaningful slice of each year's gain.

Later years

Interest-on-interest dominates. By the final year, growth is about 34% of the whole balance.

Starting balance+Contributions+Interest-on-interest=Future value
  1. StartMonth 1
  2. End of year 1$16,919
  3. Balance doublesMonth 18 (1.5 yrs)
  4. Growth overtakes your moneyNot reached in this time period
  5. Final (year 10)$106,639

Visual breakdown

Balance growth over time

Starting balance, contributions, and interest stacked to your future value.

YearYour moneyGrowthBalance
1$16,000$919$16,919
2$22,000$2,339$24,339
3$28,000$4,294$32,294
4$34,000$6,825$40,825
5$40,000$9,973$49,973
6$46,000$13,782$59,782
7$52,000$18,299$70,299
8$58,000$23,578$81,578
9$64,000$29,671$93,671
10$70,000$36,639$106,639
Show data as a table
YearYour moneyGrowthBalance
1$16,000$919$16,919
2$22,000$2,339$24,339
3$28,000$4,294$32,294
4$34,000$6,825$40,825
5$40,000$9,973$49,973
6$46,000$13,782$59,782
7$52,000$18,299$70,299
8$58,000$23,578$81,578
9$64,000$29,671$93,671
10$70,000$36,639$106,639

Your money vs growth

How much of the final balance you put in vs what interest added.

PartAmount
Your money$70,000
Interest / growth$36,639
Show data as a table
PartAmount
Your money$70,000
Interest / growth$36,639

Simple vs compound interest

The gap is the value created by interest earning interest.

YearCompoundSimple
Y1$16,919$16,893
Y2$24,339$24,205
Y3$32,294$31,938
Y4$40,825$40,090
Y5$49,973$48,663
Y6$59,782$57,655
Y7$70,299$67,068
Y8$81,578$76,900
Y9$93,671$87,153
Y10$106,639$97,825
Show data as a table
YearCompoundSimple
Y1$16,919$16,893
Y2$24,339$24,205
Y3$32,294$31,938
Y4$40,825$40,090
Y5$49,973$48,663
Y6$59,782$57,655
Y7$70,299$67,068
Y8$81,578$76,900
Y9$93,671$87,153
Y10$106,639$97,825

Nominal vs real value

Real value shows today's purchasing power after inflation.

YearNominalReal
Y1$16,919$16,426
Y2$24,339$22,941
Y3$32,294$29,554
Y4$40,825$36,273
Y5$49,973$43,107
Y6$59,782$50,066
Y7$70,299$57,160
Y8$81,578$64,398
Y9$93,671$71,791
Y10$106,639$79,349
Show data as a table
YearNominalReal
Y1$16,919$16,426
Y2$24,339$22,941
Y3$32,294$29,554
Y4$40,825$36,273
Y5$49,973$43,107
Y6$59,782$50,066
Y7$70,299$57,160
Y8$81,578$64,398
Y9$93,671$71,791
Y10$106,639$79,349

Compounding frequency comparison

Same money and rate — only how often interest is added changes.

FrequencyAPYFinal value
Annually7.00%$105,197
Semi-annually7.12%$105,966
Quarterly7.19%$106,366
Monthly7.23%$106,639
Daily7.25%$106,773
Continuous7.25%$106,777
Show data as a table
FrequencyAPYFinal value
Annually7.00%$105,197
Semi-annually7.12%$105,966
Quarterly7.19%$106,366
Monthly7.23%$106,639
Daily7.25%$106,773
Continuous7.25%$106,777

Scenario comparison

Final value under different assumptions (set them below).

ScenarioFinal value
Base case$106,639
Lower return (-2%)$94,111
Higher contribution (+50%)$149,910
Longer horizon (+10y)$300,851
Show data as a table
ScenarioFinal value
Base case$106,639
Lower return (-2%)$94,111
Higher contribution (+50%)$149,910
Longer horizon (+10y)$300,851

Compare growth scenarios

-2% return
+50%
+10 yrs
ScenarioFinal valueReal valueTotal contributedGrowthDifference vs base
Base case$106,639$79,349$70,000$36,639
Lower return (-2%)$94,111$70,028$70,000$24,111-$12,528
Higher contribution (+50%)$149,910$111,547$100,000$49,910+$43,271
Longer horizon (+10y)$300,851$166,574$130,000$170,851+$194,212

Scenarios are descriptive comparisons, not recommendations. None is labelled good or bad.

Growth schedule

Year 1$16,919
Contributions
$6,000
Interest/growth
$919
Real value
$16,426
Growth share
5%
Year 2$24,339
Contributions
$6,000
Interest/growth
$1,419
Real value
$22,941
Growth share
10%
Year 3$32,294
Contributions
$6,000
Interest/growth
$1,956
Real value
$29,554
Growth share
13%
Year 4$40,825
Contributions
$6,000
Interest/growth
$2,531
Real value
$36,273
Growth share
17%
Year 5$49,973
Contributions
$6,000
Interest/growth
$3,148
Real value
$43,107
Growth share
20%
Year 6$59,782
Contributions
$6,000
Interest/growth
$3,809
Real value
$50,066
Growth share
23%
Year 7$70,299
Contributions
$6,000
Interest/growth
$4,518
Real value
$57,160
Growth share
26%
Year 8$81,578
Contributions
$6,000
Interest/growth
$5,278
Real value
$64,398
Growth share
29%
Year 9$93,671
Contributions
$6,000
Interest/growth
$6,094
Real value
$71,791
Growth share
32%
Year 10$106,639
Contributions
$6,000
Interest/growth
$6,968
Real value
$79,349
Growth share
34%
YearStartContributionsInterest/growthEnding balanceReal valueGrowth share
1$10,000$6,000$919$16,919$16,4265%
2$16,919$6,000$1,419$24,339$22,94110%
3$24,339$6,000$1,956$32,294$29,55413%
4$32,294$6,000$2,531$40,825$36,27317%
5$40,825$6,000$3,148$49,973$43,10720%
6$49,973$6,000$3,809$59,782$50,06623%
7$59,782$6,000$4,518$70,299$57,16026%
8$70,299$6,000$5,278$81,578$64,39829%
9$81,578$6,000$6,094$93,671$71,79132%
10$93,671$6,000$6,968$106,639$79,34934%

How to use the compound interest calculator

Enter your starting balance, a regular contribution and how often you add it, your assumed annual return and compounding frequency, and a time horizon. Optional fields let you model contribution timing, annual contribution increases, a one-time deposit, inflation, fees, and taxes, or switch on goal mode to solve for what a target requires. Everything calculates in your browser — no sign-in and no personal data collected.

How to read your results

The headline is your estimated future value. Below it, the breakdown separates the money you put in (starting balance plus contributions) from the interest and growth it earned, shows the effective annual rate (APY), the inflation-adjusted real value, total fees and estimated taxes, and how the result compares with plain simple interest. Charts and a year-by-year schedule show how the balance builds, and the Excel model lets you keep the full plan.

How this calculator works

A month-by-month schedule drives every figure, so the summary, charts, year table, scenarios, and goal solver always agree.

  • Your stated rate and compounding frequency are converted into an effective monthly rate, so monthly compounding reproduces the exact effective annual rate (EAR/APY) of the frequency you chose — annual, quarterly, monthly, daily, or continuous.
  • Contributions are added at the start or end of each period based on your timing choice; beginning-of-period money earns one extra period of growth.
  • Annual contribution increases, a contribution stop year, and a one-time deposit are applied on the schedule as they occur.
  • Inflation discounts the balance back to today's purchasing power; an annual fee % and fixed annual fee are applied proportionally each month.
  • Tax can be applied to interest each year or to total growth at the end. Goal mode solves for the required contribution, return, time, or starting amount that reaches your target.
Compound interest: A = P(1 + r/n)^(n x t) With contributions: FV = P(1 + i)^m + C x [((1 + i)^m - 1) / i] Effective annual rate (APY): EAR = (1 + r/n)^n - 1 Continuous compounding: A = P x e^(r x t) Simple interest: A = P(1 + r x t) Inflation-adjusted: Real FV = Nominal FV / (1 + inflation)^t Rule of 72: years to double ~= 72 / annual return %
P
Starting amount (principal)
r
Annual interest rate (as a decimal)
n
Compounding periods per year
t
Time in years
i
Periodic rate = r / n
m
Total number of periods = n × t
C / PMT
Regular contribution each period

Worked example

A $10,000 starting balance with $500 added every month at a 7% annual return, compounded monthly, over 10 years (3% inflation) produces this estimate.

Estimated future value

$106,639

Total contributed (incl. start)

$70,000

Interest / growth earned

$36,639

Effective annual rate (APY)

7.23%

Simple-interest comparison

$97,825

Real value after inflation

$79,349

What changes if the return is different

  • Same plan at a 5% return≈ $94,100 future value
  • Base case at a 7% return$106,639 future value
  • Same plan at a 9% return≈ $121,300 future value

Same starting balance, contribution, and time horizon — only the assumed annual return changes. Returns are not guaranteed.

Mistake to avoid

Do not compare a nominal future value with today's prices without adjusting for inflation. Here the $106,639 balance is worth about $79,349 in today's money at 3% inflation — roughly a quarter less. Check the inflation-adjusted (real) value before deciding whether a projected balance will actually cover a future goal.

The Complete Guide to Compound Interest

What is compound interest?

Compound interest is interest earned on both your original principal and the interest that has already been added to the balance. Instead of earning a flat amount each period, your money earns on an ever-larger base, so growth speeds up the longer it runs. This is what people mean by interest-on-interest, and it is the single most important idea in long-term saving and investing.

The opposite is simple interest, which is calculated only on the original principal and grows in a straight line. Over a year or two the two look similar, but over decades the compounding curve pulls dramatically ahead.

How this compound interest calculator works

This tool runs a month-by-month simulation of your balance. Each month it adds any contribution, applies growth based on your rate and compounding frequency, subtracts any fees, applies tax if you chose to, and records the new balance. The summary numbers, charts, year-by-year table, scenarios, and goal solver all read from that same schedule, so they always agree to the cent.

Because the engine works in months, it can show you both a clean yearly summary and a detailed period-by-period schedule, and it can model contributions, increases, one-time deposits, fees, taxes, and inflation together — things a single textbook formula cannot capture on its own.

The compound interest formula

For a single lump sum, future value is A = P(1 + r/n)^(n x t). Here P is the starting principal, r is the annual interest rate as a decimal, n is the number of times interest compounds per year, and t is the number of years. The exponent n x t is the total number of compounding periods.

For example, $10,000 at 7% compounded monthly for 10 years is 10,000 x (1 + 0.07/12)^(12 x 10), which works out to about $20,097 — roughly double, with no contributions at all.

Monthly contributions explained

Most people do not invest a single lump and walk away — they add money regularly. Each contribution becomes part of the balance and earns its own interest from the moment it lands. The future value of a stream of equal contributions is FV = C x [((1 + i)^m - 1) / i], where C is the contribution, i is the rate per contribution period, and m is the number of contributions.

In the worked example, $500 a month for 10 years is $60,000 of contributions. Combined with the $10,000 start, you put in $70,000 — but the ending balance is about $106,639, meaning roughly $36,639 came from growth.

Compounding frequency explained

Compounding frequency is how often earned interest is added back to the balance: annually, semi-annually, quarterly, monthly, daily, or continuously. The more often interest compounds, the slightly higher the effective return, because interest starts earning interest sooner.

The effect is real but usually modest. The frequency comparison chart on this page holds the rate and time constant and varies only the frequency, so you can see exactly how much it changes the outcome — typically far less than a change in rate or time would.

APR vs APY / EAR

A nominal rate (sometimes shown as APR for borrowing) does not account for compounding within the year. The effective annual rate (EAR), shown as APY for savings, does. The conversion is EAR = (1 + r/n)^n - 1.

A 7% nominal rate compounded monthly is about a 7.23% APY. When you compare two accounts, compare their APYs, not their nominal rates — APY is the apples-to-apples figure. This calculator lets you enter either and shows the resulting APY.

Simple interest vs compound interest

Simple interest pays the same amount every period because it is always based on the original principal. Compound interest grows because it is based on the principal plus all prior interest. The longer the horizon, the wider the gap.

On this page the simple-vs-compound chart plots both paths from the same contributions. In the worked example, simple interest reaches about $97,825 while compound reaches $106,639 — the roughly $8,800 difference is value created purely by compounding.

Why starting early matters

Time is the most powerful lever in compounding because growth builds on itself. Two people who contribute the same amount can end with very different balances purely because one started earlier and gave their money more years to compound.

A classic illustration: someone who invests for ten years and then stops can sometimes finish ahead of someone who starts ten years later and contributes for far longer, simply because the early money had more time to grow. Starting now, even with a small amount, is often the highest-impact decision.

Why the later years often add more growth

In the early years of a plan, your contributions make up most of the balance and growth is a small slice. As the balance gets larger, the interest it throws off each year grows too, until eventually a single year of growth can exceed a whole year of contributions.

That is why the balance-growth chart curves upward rather than rising in a straight line, and why patience is rewarded: the biggest gains usually come at the end of a long horizon, not the beginning.

Rule of 72 explained

The Rule of 72 is a shortcut for estimating how long money takes to double: divide 72 by the annual return percentage. At 6% money doubles in about 12 years, at 8% in about 9 years, and at 9% in about 8 years.

It is an approximation that works best for rates between roughly 5% and 12%, and it ignores contributions. Use it for quick intuition; use the full schedule on this page for an accurate doubling point.

Inflation-adjusted future value

A balance in the future is not worth as much as the same number today, because prices rise. To compare fairly, you discount the future value back to today's money: Real FV = Nominal FV / (1 + inflation)^t.

In the worked example, the $106,639 nominal balance is worth about $79,349 in today's purchasing power at 3% inflation. Looking at the real value keeps a long-term plan honest about what it will actually buy.

How fees reduce compounding

Fees do not just cost you the fee — they cost you all the future growth that money would have earned. A 1% annual fee may sound small, but over decades it can quietly remove a large share of the final balance because it compounds against you every year.

Enter an annual fee percentage or a fixed annual fee to see the impact. Comparing a low-fee and high-fee scenario is one of the most useful things this calculator can show.

How taxes can change real results

Depending on the account and country, growth may be taxed each year as it is earned, taxed only when you withdraw, or sheltered in a tax-advantaged account. Each treatment produces a different after-tax result.

The optional tax setting lets you apply a rate to interest annually or to total growth at the end so you can see an after-tax estimate. It is a simplified model — for your specific tax situation, account type, and jurisdiction, confirm with a qualified professional.

Savings account vs investment return assumptions

Different goals justify different return assumptions. A savings account or certificate of deposit might pay a low, relatively stable rate, while a diversified long-term investment portfolio has historically averaged more but with year-to-year ups and downs, including losses.

Choose a rate that matches what you are actually modelling, and remember that a higher assumed return also carries higher risk. This tool does not recommend any rate — it simply projects the one you enter.

Worked example

Start with $10,000, add $500 every month, assume a 7% annual return compounded monthly, and run it for 10 years. You contribute $60,000 over the decade, so with your starting balance you have put in $70,000.

The estimated future value is about $106,639. That means roughly $36,639 — more than a third of the ending balance — came from growth rather than from your own deposits. The effective annual rate is about 7.23%, and at 3% inflation the balance is worth about $79,349 in today's money.

Common mistakes

The most common mistakes are ignoring inflation, forgetting fees, assuming an unrealistically high return, and underestimating how much time matters. Another is comparing accounts by nominal rate instead of APY, which hides the effect of compounding frequency.

A good habit is to model a base case and a more conservative case side by side using the scenario tools on this page, so your plan does not depend on everything going right.

Limitations of this calculator

This calculator assumes your rate, contributions, fees, inflation, and tax rate stay constant unless you change them. Real returns vary, sometimes sharply, and a single average rate cannot capture the sequence of good and bad years that a real portfolio experiences.

The tax model is a simplified estimate, not a tax return, and it does not account for account-specific rules or contribution limits. Treat every figure as a planning estimate rather than a prediction.

When to use a professional adviser

A calculator is excellent for understanding the mechanics and running what-ifs, but it is not a substitute for personalised advice. If you are making a major decision — choosing accounts, planning for retirement, handling a windfall, or weighing tax strategies — a qualified financial or tax professional can account for your full situation.

Use this tool to arrive informed: bring your assumptions, scenarios, and questions, and let a professional help you pressure-test the plan.

How to use the Excel download

The Download Excel model button builds a workbook with six sheets: your inputs, a results summary, a yearly schedule, a full period-by-period schedule, a scenario comparison, and plain-English formula notes. It opens in Excel, Google Sheets, and Apple Numbers.

Use it to keep a record of a plan, to tweak numbers offline, or to share assumptions with a partner or adviser. The CSV download gives you just the schedule, and Copy results gives you a quick text summary to paste anywhere.

Common Uses

Practical ways to use this calculator. Each is a short walkthrough, not financial advice.

Monthly savings growth

The most common use is projecting a regular saving habit. Enter your current balance, the amount you add each month, an assumed rate, and a horizon, and the calculator shows how the balance builds and how much of it comes from growth rather than your own deposits. For example, $200 a month at 5% over 15 years contributes $36,000 but can finish noticeably higher once interest compounds. Try a few rates and amounts to see which lever — saving more or earning more — moves your result the most for your situation.

Retirement planning

For long horizons, compounding does most of the heavy lifting, so this tool is useful for a first-pass retirement projection. Set a 20-to-40-year horizon, add your monthly contribution, and use the annual contribution increase to model pay rises over a career. Switch on inflation to see the balance in today's money, which keeps a long plan honest about real purchasing power. For employer matching, vesting, account limits, and withdrawal rules, pair this with a dedicated retirement calculator — those details sit outside a general compounding model.

Investment goal planning

When you have a target in mind — a house deposit, a sabbatical, a child's milestone — turn on goal mode. Enter the amount you want and solve for the monthly contribution, the return, the time, or the starting balance it would require. The solver flags targets that need an unrealistically high return so you can adjust the plan rather than rely on luck. Treat the required figures as planning estimates: they show what the math demands under your assumptions, not a recommendation to take on more risk.

Education fund planning

Saving for education usually has a fixed deadline, which makes the time horizon the key input. Set the number of years until the funds are needed, add your regular contribution, and choose a rate that matches how the money is held — a conservative rate for cash-like savings, a higher (and riskier) one for a long-dated investment account. Because tuition costs tend to rise, switch on inflation to compare the projected balance against future costs in today's money rather than headline figures alone.

Emergency fund growth

An emergency fund is about access and stability rather than maximum return, so model it with a modest, realistic rate and frequent contributions. Use the calculator to see how long steady deposits take to reach a target of, say, three to six months of expenses, and how a high-yield savings rate compares with a near-zero one over a couple of years. The schedule and goal mode together show when your buffer reaches a comfortable level, which is often more useful than the final balance.

Comparing simple vs compound interest

The calculator runs a parallel simple-interest track — interest on your principal only, never on prior interest — and plots it against the compound path. The gap between the two lines is the value created purely by compounding, and it widens the longer the money runs. This is the clearest way to see why interest-on-interest matters: over one or two years the difference is small, but over decades the compound curve pulls well ahead. If you only need interest on a fixed principal with no reinvestment, use the simple interest calculator instead.

Understanding inflation impact

A future balance buys less than the same number today because prices rise over time. Enter an inflation rate and the calculator discounts the projected balance back to today's purchasing power, shown alongside the nominal figure and on the nominal-versus-real chart. This matters most for long horizons: at 3% inflation, money roughly halves in real value over about 24 years. Looking at the real value stops a long plan from feeling more comfortable than it should and keeps the comparison with future costs fair.

Limitations and Assumptions

  • Returns, contributions, inflation, fees, and taxes are assumed to stay constant unless you change them; real markets and accounts vary year to year.
  • Tax handling is a simplified estimate and does not model brackets, account types, capital-gains rules, or jurisdiction-specific treatment.
  • This is an educational projection, not financial, investment, or tax advice, and investment returns are not guaranteed.

When this calculator may not be enough

This calculator is a clear planning tool, but some situations need a more specialised model or professional input. It may not be enough for:

  • Highly volatile investments, where real returns swing year to year instead of following one steady rate.
  • Country-specific tax calculations, account types, contribution limits, and capital-gains rules.
  • Loan amortization or repayment schedules, which work differently from a growing balance.
  • Day-to-day or daily trading returns, which this constant-rate model does not attempt to predict.
  • Guaranteed deposit products with special rules, penalties, or stepped rates.
  • Retirement plans with an employer match, vesting, or withdrawal restrictions.
  • Complex portfolios with changing asset allocation or rebalancing over time.

Frequently Asked Questions

What is compound interest?

Compound interest is interest earned on both your original principal and the interest already added to the balance. Because each period earns interest on a larger base, the balance can grow faster over time — the effect often called interest-on-interest.

How is compound interest calculated?

For a lump sum, future value is A = P(1 + r/n)^(n x t), where P is the starting amount, r is the annual rate, n is how many times a year interest compounds, and t is the number of years. When you add regular contributions, each contribution also earns interest from the time it is deposited, so the final balance is your starting amount plus contributions plus the growth on both.

What is the compound interest formula?

The core formula is A = P(1 + r/n)^(nt). With regular contributions you add the future value of an annuity: FV = P(1 + i)^m + C x [((1 + i)^m - 1) / i], where i is the rate per contribution period, C is the contribution, and m is the number of contributions.

Can I include monthly contributions?

Yes. Enter a contribution amount and choose weekly, biweekly, monthly, quarterly, or yearly. You can also set whether contributions are added at the beginning or end of each period, increase them by a set percentage each year, stop them after a number of years, and add a one-time deposit.

Can I use this for SIP or monthly investing?

Yes. A systematic investment plan (SIP) is simply a fixed amount invested at regular intervals, which is exactly what the contribution field models. Set your monthly (or weekly, quarterly, or yearly) amount, choose an assumed annual return and compounding frequency, and the calculator projects the future value. You can also increase the contribution each year and switch the currency display — the math is identical in any currency.

What is the difference between simple and compound interest?

Simple interest is calculated only on the original principal, so it grows in a straight line. Compound interest is calculated on the principal plus previously earned interest, so it grows faster the longer it runs. This calculator shows both side by side, and the gap between them is the value created purely by compounding.

Is compound interest the same as investment return?

Not exactly. Compound interest describes how a fixed, positive rate grows when earnings are reinvested. An investment return is the actual gain or loss of an asset, which varies year to year and can be negative. This calculator applies one constant rate you choose, so it models the compounding mechanics well but cannot capture real market ups and downs. Treat the rate you enter as a planning assumption, not a guaranteed return.

What is APY or Effective Annual Rate?

APY (annual percentage yield) and EAR (effective annual rate) both describe the true annual return after compounding is taken into account. EAR = (1 + r/n)^n - 1. A 7% nominal rate compounded monthly is about a 7.23% APY. APY lets you compare accounts or investments that compound at different frequencies on an equal footing.

Is monthly compounding better than annual compounding?

Slightly. More frequent compounding adds interest back to the balance sooner, so it starts earning its own interest earlier and the effective annual rate (APY) is a little higher. The gap is usually small next to the rate, contribution amount, and time horizon: at 7% on $10,000, monthly compounding produces about a 7.23% APY versus 7.00% for annual. Use the compounding-frequency comparison chart on this page to see the exact difference for your numbers.

Does compounding daily make a big difference?

Compounding more often increases the return, but the effect is usually small compared with the rate, the contribution amount, and time. At 7% on $10,000 for 10 years, moving from annual to daily compounding adds roughly a percent or two to the final balance — far less than raising the rate or extending the horizon would.

What is the Rule of 72?

The Rule of 72 is a quick estimate of how long money takes to double: divide 72 by the annual return percentage. At 8%, money roughly doubles in 9 years; at 6%, about 12 years. It is an approximation for mental math, not an exact figure.

Why does starting early matter?

A longer time horizon gives interest more periods to earn interest on itself, so the later years of a long plan often add far more growth than the early years. Starting earlier — even with smaller contributions — can beat starting later with larger ones, because time does much of the work.

Does this calculator include taxes?

Optionally. You can apply a tax rate to interest each year, or to total growth at the end, to see an after-tax estimate. The tax handling is a simplified approximation and does not replace advice from a tax professional for your specific situation and account type.

Does this calculator include inflation?

Yes. Enter an inflation rate and the calculator shows the inflation-adjusted (real) value — what the future balance would be worth in today's purchasing power — alongside the nominal value.

Does this calculator include fees?

Yes. You can enter an annual fee as a percentage of the balance and a fixed annual fee. Fees are applied proportionally each month and reduce the growth, which over decades can make a meaningful difference to the final balance.

Can I download the results in Excel?

Yes. The Download Excel model button creates a workbook with your inputs, a results summary, the full yearly and period-by-period schedules, a scenario comparison, and formula notes. You can also download the schedule as a CSV or copy a text summary of the results.

Why are investment returns not guaranteed?

Market returns vary year to year and can be negative. This tool assumes a constant return that you enter, which is useful for planning but does not predict what any account or investment will actually earn. Treat the result as an estimate, not a promise.

Can compound interest work against me in debt?

Yes. The same math that grows savings can grow debt. On credit cards and other loans that compound, unpaid interest is added to the balance and then itself accrues interest, so a balance can grow quickly if it is not paid down. Compounding helps you when you are the saver and works against you when you are the borrower.

Why are my results different from a bank or broker statement?

A real statement reflects the actual interest your account paid, the exact dates money moved in and out, fees and taxes specific to your account, and — for investments — real market movements. This calculator assumes one steady rate, even contributions, and simplified fees and tax, so it is a clean planning estimate rather than a record of what happened. Small differences are normal: use this tool for projections and your statement for actuals.

Is this calculator country-specific?

No. The math is universal. The currency selector only changes how numbers are displayed and does not apply any country's tax rules, account limits, or interest regulations. Check local rules for the savings or investment account you are modelling.

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How CalculatorMatters checks this calculator

  • Formula reviewed against standard compound-interest, annuity, APY/effective-annual-rate, and inflation math.
  • Outputs tested against worked examples calculated by hand and against the U.S. SEC Investor.gov compound interest calculator.
  • Results are presented as estimates, not guarantees — the tool does not predict actual investment returns.
  • Sources are checked against primary government and regulatory references (SEC, CFPB, BLS).
  • Found an error? Email corrections@calculatormatters.com and we will review and correct it.

Last reviewed: June 2026 · Method: Formula-based estimate with a step-by-step, month-by-month projection.

Maintained by the CalculatorMatters Editorial Team. We are not certified financial planners; this tool is educational and does not provide personal financial advice.

Sources & References

Figures on this page are checked against primary, authoritative sources. Links open in a new tab.

Investment disclaimer

Returns are assumptions, not guarantees. Actual results may vary because of market performance, taxes, fees, inflation, and timing. This is an educational projection, not investment advice.

Built and maintained by Calculator Matters, an independent calculator project. Method checked against published formulas and primary sources · Educational estimate, not professional advice · How we calculate · Found an error? corrections@calculatormatters.com