BMR vs. TDEE: the Mifflin-St Jeor formula, worked by hand

Every calorie target — for losing weight, gaining muscle, or just maintaining — starts from the same two numbers: how much energy your body burns doing nothing, and how much it burns doing everything else. Those are BMR and TDEE, and the standard formula for the first one is short enough to run on paper.

The method

BMR (basal metabolic rate) is the energy your body would burn over 24 hours if you did nothing but lie still. The Mifflin-St Jeor equation estimates it from weight, height, age and sex:

• Men: BMR = 10 × kg + 6.25 × cm − 5 × age + 5
• Women: BMR = 10 × kg + 6.25 × cm − 5 × age − 161

TDEE (total daily energy expenditure) scales BMR up for activity: TDEE = BMR × activity multiplier. The multiplier is a rough band, not a measurement — about 1.2 for sedentary, 1.375 for light activity (exercise 1–3 days a week), 1.55 for moderate, 1.725 for very active, and 1.9 for an athlete training daily.

A worked example

A 29-year-old woman, 68 kg, 165 cm tall, who exercises lightly — activity multiplier 1.375.

1. 10 × 68 = 680
2. 6.25 × 165 = 1,031.25
3. 5 × 29 = 145
4. BMR: 680 + 1,031.25 − 145 − 161 = 1,405.25 — about 1,405 kcal/day at complete rest.
5. TDEE: 1,405.25 × 1.375 = 1,932.22 — about 1,932 kcal/day with light activity folded in.

The gap between the two — roughly 527 kcal here — is entirely the activity multiplier's doing. Swap in 1.55 (moderate) instead of 1.375 and TDEE becomes 1,405.25 × 1.55 = 2,178.14, about 246 kcal higher on the same body, same BMR, just a more active week.

What this doesn't include

Mifflin-St Jeor is a population average, not a metabolic measurement of you specifically — it can be off by a meaningful margin for people with unusual muscle mass, medical conditions affecting metabolism, or body compositions far from the study population it was derived from. The activity multiplier is a self-reported band, not a wearable-tracked number. Treat the TDEE figure as a starting point to adjust from real-world weight trends over a few weeks, not a number to hit exactly. This is informational only, not medical or dietary advice.

Run your own numbers

The free BMR / TDEE tool takes weight, height, age, sex and an activity multiplier and returns both figures instantly, entirely on your device.