How It Works
BMR is calculated using the Mifflin-St Jeor equation (1990), the most accurate equation for the general population according to multiple validation studies.
BMR (male) = 10W + 6.25H − 5A + 5 | BMR (female) = 10W + 6.25H − 5A − 161 | TDEE = BMR × Activity Factor | (W = kg, H = cm, A = age)
- Weight is converted from pounds to kilograms (÷ 2.2046) and height from inches to centimeters (× 2.54).
- TDEE (Total Daily Energy Expenditure) multiplies BMR by an activity multiplier: Sedentary 1.2, Light 1.375, Moderate 1.55, Active 1.725, Extra Active 1.9.
- Weight loss target uses a 500 calorie deficit, which creates approximately a 0.5–1 lb/week loss for most people.
- Weight gain target uses a 500 calorie surplus for approximately 0.5–1 lb/week lean mass gain.
Worked Example
A 30-year-old male, 5’7" (67"), 155 lbs, moderately active (3–5 days/week).
Activity
Moderately Active (×1.55)
TDEE (Maintenance)
2,514 cal/day
Weight Loss Target
2,014 cal/day
Weight Gain Target
3,014 cal/day
To maintain weight, eat ~2,514 calories. For fat loss (roughly 0.5–1 lb/week for many people), target about 2,014 calories. For lean-mass gain, target about 3,014 calories and prioritize protein. Actual results vary with metabolism, adherence, body composition, water balance, and adaptation, so adjust based on your own progress over a few weeks.
How to Use a Calorie Calculator to Set a Realistic Daily Target
What this calculator measures
A calorie calculator estimates how much energy your body needs in a day. It starts from your Basal Metabolic Rate (BMR) — the calories you would burn at complete rest — and scales that up by an activity factor to reach your Total Daily Energy Expenditure (TDEE), the number that maintains your current weight.
It is a useful starting point for anyone planning to lose fat, hold steady, or gain weight, and for anyone who simply wants a sense of how much they should be eating before they begin tracking food.
How the Mifflin-St Jeor equation works
This tool uses the Mifflin-St Jeor equation, widely regarded as one of the most reliable BMR formulas for the general adult population. It takes four inputs — weight, height, age, and sex — because each affects resting energy use. Larger bodies burn more, and resting burn tends to decline gradually with age.
Your weight and height are converted to metric inside the formula. The result is your BMR, which is then multiplied by an activity factor between 1.2 (sedentary) and 1.9 (extra active) to estimate the calories you actually use across a normal day.
Turning your TDEE into a goal
Once you have your TDEE, your goal is just a shift away from it. To lose weight, eat below your TDEE — a deficit of roughly 500 calories a day targets about one pound (0.45 kg) of loss per week for many people. To gain weight, eat above it, ideally paired with resistance training so the surplus builds muscle rather than only fat.
The reference table on this page lays out your maintenance calories across every activity level, and the goal figures show sensible loss and gain targets so you can pick the path that matches your plan.
How to interpret the numbers
Treat the output as an educated estimate, not a precise prescription. The single most useful way to read it is as a baseline to test: eat near the target for two to four weeks, track your weight trend, and adjust based on what actually happens on the scale and in the mirror.
If you are losing or gaining faster or slower than you intended, nudge calories by 100–200 per day rather than making large jumps. Real-world feedback always beats a formula.
Common mistakes to avoid
The most frequent error is overestimating activity level. Many people who exercise a few times a week are closer to "lightly active" than "very active" once a full day of sitting is accounted for. Choosing too high a multiplier inflates your target and can quietly stall fat loss.
Other common mistakes include eating below your BMR to speed up results, forgetting to log drinks, oils, and snacks, and never recalculating after your weight changes. All three undermine the accuracy of the plan.
Why the 500-calorie rule is a starting point, not a guarantee
The familiar "cut 500 calories a day to lose a pound a week" guideline comes from the idea that a pound of body fat stores about 3,500 calories. It is a reasonable first estimate, but your body is not a fixed machine: as you eat less and lose weight, your resting metabolism falls and the original deficit quietly shrinks. That is why weight loss almost always decelerates after the first few weeks rather than continuing in a straight line.
The U.S. National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) built its Body Weight Planner around this "dynamic energy balance" precisely because the old 3,500-calorie rule overpromises. Use the targets here to begin, then let your real weight trend over two to four weeks tell you whether to hold steady or adjust by another 100–200 calories.
Limitations and when to seek professional guidance
BMR equations carry a margin of error of roughly 10–15% for any individual and cannot account for body composition, so a very muscular person will burn more than the formula predicts. Medical conditions such as thyroid disorders can also meaningfully change your needs.
This calculator is educational and is not a substitute for personalised advice. If you are pregnant or breastfeeding, managing a health condition, recovering from an eating disorder, or planning a very low-calorie diet, consult a qualified healthcare professional or registered dietitian before making changes.