BMR vs TDEE: How Many Calories You Actually Need (and Why)

Your BMR is the calories you’d burn lying in bed all day; your TDEE is that number multiplied by how much you actually move — and TDEE is the one that decides whether you lose, hold, or gain weight. Get your BMR from the Mifflin–St Jeor equation, multiply by an activity factor, then eat below it to lose or above it to gain. Run your own numbers in the TDEE & calorie calculator — everything below is the reasoning behind it.

BMR and TDEE, in one picture

Step 1 — BMR from Mifflin–St Jeor

Basal metabolic rate is what your body spends just staying alive: keeping your heart beating, your lungs working, your cells repairing. It’s the biggest slice of most people’s daily burn — usually 60–70% of the total. The Mifflin–St Jeor equation, published in 1990, is the one dietitians reach for because it tracks measured metabolism more closely than the older Harris–Benedict:

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

Work it for a 30-year-old man, 75 kg, 175 cm: 750 + 1093.75 − 150 + 5 = 1,699 calories a day at complete rest. If you think in pounds and inches, the calculator converts (1 lb = 0.4536 kg, 1 in = 2.54 cm) before applying the formula, so you don’t have to.

Step 2 — scale it to your life with an activity factor

Almost nobody spends the day at rest, so BMR alone understates your needs. Multiply by an activity factor to get TDEE:

Activity level	Factor	Who it’s for
Sedentary	1.2	Desk job, little or no exercise
Light	1.375	Light exercise 1–3 days/week
Moderate	1.55	Moderate exercise 3–5 days/week
Active	1.725	Hard exercise 6–7 days/week
Very active	1.9	Physical job or twice-daily training

Our example man at the moderate factor: 1,699 × 1.55 ≈ 2,633 calories a day. That’s his TDEE — the calories that keep his weight steady.

The single most common mistake here is over-rating yourself. A gym session three times a week on top of a desk job is light-to-moderate, not active. When you’re between two levels, choose the lower one: it’s easier to add food later than to explain why a too-generous estimate stalled your progress.

Step 3 — turn TDEE into a goal

TDEE is your maintenance line. To change weight, create a gap:

• To lose: eat below TDEE. A pound of body fat stores roughly 3,500 calories, so a 500 kcal/day deficit ≈ 1 lb (0.45 kg) a week; 250/day ≈ half a pound. In our example, ~2,133 kcal/day targets a half-kilo weekly loss.
• To maintain: eat at your TDEE.
• To gain: eat above it. A 500/day surplus supports roughly a pound a week, though for muscle gain a smaller 250–300 surplus wastes less as fat.

Two guardrails. Don’t drop below your BMR for extended periods — that’s the floor your organs need. And bigger deficits aren’t better: past ~1,000/day you start burning muscle and the plan gets hard to keep. Once you know your target calories, split them into protein, carbs and fat with the macro calculator, and sanity-check your goal weight against a healthy range with the ideal weight calculator.

Why the number is an estimate, not a verdict

Every formula on this page is a population average fitted to your height, weight, age and sex. It can’t see your muscle mass (metabolically pricier than fat), your thyroid, or your NEAT — the calories you burn fidgeting, pacing and generally not sitting still, which varies by hundreds of calories between people. Realistically your true TDEE sits within about ±10–15% of the estimate.

So use it the way a coach would: eat at the target for two to three weeks, watch the trend on the scale (not any single day, which is mostly water), and adjust by 100–200 calories if reality and the math disagree. The formula gives you a smart starting point; your own results are the calibration. This is general information, not medical advice — check with a professional before big changes, especially if you have a health condition.

Quick summary

BMR is what you burn at rest (Mifflin–St Jeor: 10×kg + 6.25×cm − 5×age ± sex constant). TDEE is BMR times an activity factor from 1.2 to 1.9, and it’s the number that governs your weight: eat ~500 below it to lose about a pound a week, at it to maintain, above it to gain. Pick your activity level honestly, never live below your BMR, and treat the result as a two-week experiment to refine. Get your own figures — privately, in your browser — from the TDEE & calorie calculator, then plan the plate with the macro calculator.

Sources: Mifflin MD, St Jeor ST, et al. — A new predictive equation for resting energy expenditure (Am J Clin Nutr, 1990) · NIH — Body Weight Planner · standard dietetics activity-factor conventions. General information only, not medical advice.