How TDEE is calculated
This uses the Mifflin-St Jeor equation, which first estimates your BMR — the calories you burn at complete rest:
- Men: 10×weight(kg) + 6.25×height(cm) − 5×age + 5
- Women: 10×weight(kg) + 6.25×height(cm) − 5×age − 161
It then multiplies that BMR by an activity factor between 1.2 and 1.9 to estimate your full daily burn.
Worked example: a 30-year-old woman weighing 65 kg at 165 cm, moderately active. Her BMR is 10×65 + 6.25×165 − 5×30 − 161 = 650 + 1,031 − 150 − 161 ≈ 1,370 kcal. Her TDEE is 1,370 × 1.55 ≈ 2,124 kcal/day. You can check that arithmetic by hand, and we would encourage it — a calculator that will not show its working is asking for trust it has not earned.
Where this formula comes from
The equation was published in 1990 by Mark Mifflin, Sachiko St Jeor and colleagues in the American Journal of Clinical Nutrition. It replaced the 1919 Harris-Benedict equation as the default in clinical dietetics because it matched measured resting energy expenditure more closely in contemporary populations — Harris-Benedict was derived from a much smaller and less representative sample and tends to over-estimate.
Choosing your activity level honestly
This input moves the result more than anything else, and it is where most people go wrong. Look at the figure above: the same person's estimate spans nearly 1,000 calories from sedentary to very active. The common error is optimism — counting three gym sessions a week as "active" when the other 165 hours are spent sitting.
- Sedentary (1.2) — desk job, no structured exercise. This describes far more people than choose it.
- Light (1.375) — light exercise one to three days a week.
- Moderate (1.55) — moderate exercise three to five days a week.
- Active (1.725) — hard exercise six or seven days a week.
- Very active (1.9) — daily hard training, or a physically demanding job on top of training.
If you are between two levels, pick the lower one. It is easier to add calories when you are losing faster than intended than to explain away weeks of no progress.
Using TDEE for your goal
- Lose fat: eat roughly 300–500 kcal below TDEE, which produces about 0.3–0.5 kg of loss per week.
- Maintain: eat around TDEE and adjust based on the trend over a month.
- Build muscle: eat roughly 200–400 kcal above TDEE alongside resistance training. Larger surpluses mostly add fat.
The macro calculator splits whichever number you land on into protein, carbohydrate and fat.
Treat the number as a hypothesis
The only reliable way to find your real maintenance level is to eat at a consistent estimate for two to three weeks, weigh yourself under consistent conditions, and see which way the weekly average trends. If it is flat, that is your maintenance. If it is falling when you meant to maintain, the estimate was low. This empirical check beats any equation, because it measures you rather than predicting a population average.
Expect to repeat it. As you lose weight you become a smaller body that costs less to run, so maintenance falls and a target that worked at the start of a fat-loss phase will be too generous 10 kg later.