Practical guide
How to Calculate Daily Calorie Needs
Estimate maintenance calories using activity level and BMR-based methodology.
Quick Answer
Step-by-Step Method
- Convert weight to kilograms and height to centimetres.
- Apply the Mifflin-St Jeor formula for your sex to get BMR — the energy your body uses at complete rest.
- Pick an activity factor: 1.2 sedentary, 1.375 light exercise, 1.55 moderate, 1.725 heavy, 1.9 very heavy.
- Multiply BMR by the activity factor. The result is your estimated total daily energy expenditure, or maintenance calories.
Worked Example
A 32-year-old woman weighing 65 kg at 168 cm: BMR = (10 × 65) + (6.25 × 168) − (5 × 32) − 161 = 650 + 1,050 − 160 − 161 = 1,379 kcal. With light exercise twice a week (factor 1.375), maintenance ≈ 1,379 × 1.375 = 1,896 kcal per day.
Detailed Explanation
Mifflin-St Jeor has been the preferred prediction equation since a 2005 American Dietetic Association review found it more accurate than the older Harris-Benedict formula for most adults. Even so, it is a population regression: individual results scatter roughly ±10% around the prediction, and further for people at the extremes of body composition. Treat the output as a starting hypothesis, not a measurement.
The activity multiplier is where most of the error enters, because people systematically overestimate their own activity. The gap between 1.375 and 1.55 on the example above is about 240 calories a day — enough to be the entire difference between slow gain and slow loss. If you are unsure, choose the lower factor and adjust upward based on what actually happens to your weight.
The honest way to use any calorie estimate is as a two-week experiment. Eat at the estimated maintenance level, weigh yourself under consistent conditions, and track the trend rather than daily readings, which swing with water and glycogen. If weight is stable, the estimate was right for you. If it moves, adjust by 100–200 calories and repeat. Your own data beats any formula.
Use the Calculator
Run your real values in the interactive tool and review assumptions before taking action.
Open related calculatorFAQ
What is the difference between BMR and TDEE?
BMR is the energy your body burns at complete rest, keeping organs running. TDEE is BMR plus everything else — movement, exercise, and digestion. TDEE is what you should compare your food intake against.
How large a deficit should I use to lose weight?
A deficit of roughly 10–20% below maintenance is commonly used, which usually means about 0.5–1% of body weight lost per week. Very steep deficits raise the share of weight lost as muscle rather than fat.
Why do two calculators give me different numbers?
Different tools use different equations — Mifflin-St Jeor, Harris-Benedict, Katch-McArdle — and different activity multipliers. Spreads of 100–300 calories between reputable calculators are normal and reflect genuine uncertainty in the estimate.