How It Works
Future Equivalent Cost applies compound inflation to find how much you will need to spend in future dollars to maintain the same purchasing power.
Future Cost = PV × (1 + r)^t | Purchasing Power = PV ÷ (1 + r)^t | where r = inflation rate, t = years
- Real purchasing power shows the real value of today’s money in future terms — a $1,000 bill stored under a mattress for 10 years at 3% inflation is only worth $744 in real terms.
- Cumulative inflation is the total percentage price increase over the full period.
- Both calculations use the compound growth formula.
Worked Example
You want to know what $1,000 today will be worth after 10 years at 3% average inflation.
Future Equivalent Cost
$1,343.92
Cumulative Inflation
34.4%
To buy the same goods that cost $1,000 today, you’ll need $1,344 in 10 years. Alternatively, $1,000 in 10 years will only buy what $744 buys today — a 25.6% loss in purchasing power.
Inflation: Why Idle Money Loses Ground
Two views of the same erosion
Inflation is the steady rise in prices that quietly shrinks what a dollar buys. This tool shows it from two directions: the Future Equivalent Cost is how much you will need later to buy what a set amount buys today, and the Real Value of Today’s Money is what a future sum is worth in today’s purchasing power.
They are the same erosion seen from opposite ends. At 3% over ten years, $1,000 of spending becomes about $1,344 — you need $344 more just to stand still — while $1,000 received in ten years buys only what about $744 buys now.
It compounds — just like interest, but against you
Inflation is not a flat subtraction; it compounds. Each year’s price rise lands on top of the last, so the gap between the two columns in the table widens steadily rather than evenly. The longer the horizon, the more dramatic the drift — which is exactly why a sum that feels comfortable today can fall short decades out.
That is the same mathematics as compound interest, simply pointed the wrong way. Understanding it is the difference between a retirement target that holds up and one that is quietly too small.
Do not assume one rate forever
Real inflation jumps around — it ran far above its long-run average in 2021–2022 and is milder in calm years. Use a long-run average (historically around 2–3%) for distant horizons and a current figure for near-term planning, rather than locking in whatever the latest headline rate happens to be.
Watch the category, too. The general CPI is an average basket; costs like tuition and medical care have often risen faster, so applying the headline rate to those expenses understates the squeeze.
The only real defence is real return
You cannot stop inflation, but you can outrun it. Money parked in an account paying near zero loses ground every year; money in assets that tend to grow at least as fast as prices preserves or builds purchasing power. What matters is the real return — your nominal return minus inflation.
For big future goals, plan in future dollars (the Future Equivalent Cost) rather than today’s sticker price, so you size the target to what it will actually cost and do not quietly under-save.
What this leaves out
This uses a single constant rate as a stand-in for a complex, shifting basket of prices. It does not model changes in your personal spending mix, income growth that can offset inflation, or taxes.
Treat the figures as illustrative rather than a forecast. Official CPI data is published by the US Bureau of Labor Statistics, and the inflation component of US savings bonds uses the same CPI-U series.
Sources & References
Figures on this page are checked against primary, authoritative sources. Links open in a new tab.