BMR to TDEE: The Formula Behind Every Calorie Target

A diet app asks for weight, height, age and an activity level, then hands back a daily calorie number with no explanation. That number comes from two steps done in order: a formula for basal metabolic rate, and a multiplication by how active you actually are. Both steps are arithmetic you can do on paper.

The method: BMR, then scale it up

Basal metabolic rate (BMR) is the energy a body burns doing nothing — lying still, organs running, no activity. This tool uses the Mifflin-St Jeor equation, the version most dietitians default to today:

BMR (men) = 10 × kg + 6.25 × cm − 5 × age + 5

BMR (women) = 10 × kg + 6.25 × cm − 5 × age − 161

Total daily energy expenditure (TDEE) — what the body burns in a normal day, not lying still — is BMR scaled by an activity multiplier:

TDEE = BMR × activity multiplier

The activity multipliers

• 1.2 — sedentary (desk job, little to no exercise)
• 1.375 — light activity (exercise 1–3 days a week)
• 1.55 — moderate activity (exercise 3–5 days a week)
• 1.725 — very active (exercise 6–7 days a week)
• 1.9 — athlete (hard training daily, sometimes twice a day)

A worked example: a 30-year-old woman

65 kg, 165 cm, age 30, light activity (1.375). Work the BMR formula term by term: 10 × 65 = 650; 6.25 × 165 = 1,031.25; 5 × 30 = 150. Combine them in order: 650 + 1,031.25 − 150 − 161 = 1,370.25 kcal — the estimated burn at complete rest.

Scale that up for activity: 1,370.25 × 1.375 = 1,884.09 kcal (1,884.09375 exactly) — a starting daily calorie target for holding steady at that activity level.

A second example: same method, a different body and a different multiplier

80 kg, 180 cm, age 35, male. 10 × 80 = 800; 6.25 × 180 = 1,125; 5 × 35 = 175. 800 + 1,125 − 175 + 5 = 1,755 kcal at rest — the same formula, just the +5 sex term instead of −161.

At moderate activity (1.55): 1,755 × 1.55 = 2,720.25 kcal. At sedentary (1.2), same body, same BMR: 1,755 × 1.2 = 2,106 kcal. That's a 614.25-calorie gap between two activity guesses on an identical body — in practice, the activity multiplier is usually where a calorie target goes wrong, not the BMR formula, because it's an estimate of behavior rather than a measurement of anything physical.

Why this is a starting point, not a verdict

TDEE is a maintenance estimate: eat close to it and weight should hold roughly steady; eat under it for a deficit, over it for a surplus. But both the equation and the multiplier are population averages, not a measurement of one body on one day — two people with identical inputs can have genuinely different real-world energy use. This is informational only, not medical or dietary advice. The way to find a real number is to eat at the estimate for two or three weeks, track the scale trend, and adjust the target based on what actually happened, not the formula alone.

What the tool adds

The formula above is all you need, on paper, to get a starting BMR and TDEE. The tool's job is just speed and fewer arithmetic slips: enter weight, height, age, sex and an activity multiplier, and it runs both calculations instantly, entirely on your device.