CalcaTools

BMR Calculator

A BMR calculator estimates your Basal Metabolic Rate — the number of calories your body burns at complete rest to keep core organs running. It uses the Mifflin-St Jeor equation, the most accurate predictive formula for adults, and serves as the foundation for total daily energy expenditure (TDEE) and any calorie target.

Last updated: June 2026 · Free · No sign-up required

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Results

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Quick reference

Activity multipliers (BMR x factor = maintenance calories):

Activity levelMultiplier
Sedentary (little exercise)1.2
Light (1–3 days/wk)1.375
Moderate (3–5 days/wk)1.55
Active (6–7 days/wk)1.725
Very active (physical job)1.9

science Mifflin-St Jeor

Most accurate predictive BMR equation for healthy adults — recommended by the American Dietetic Association.

restaurant Diet baseline

Your BMR is the floor below which you should not eat. Cuts, bulks, and maintenance all reference TDEE = BMR × activity factor.

fitness_center Track over time

BMR drops about 1–2% per decade after age 20 and falls further if you lose muscle. Recheck quarterly when actively cutting.

compare_arrows Compare formulas

Run Harris-Benedict and Katch-McArdle (LBM-based) to triangulate. They typically agree within 5%.

Interpretation guide

BMR vs related terms:

TermMeaning
BMRCalories burned at complete rest
TDEEBMR x activity factor
DeficitEat below TDEE to lose weight
SurplusEat above TDEE to gain weight

lightbulb A real-world example — a 35-year-old woman, 5'6", 150 lb

You're a 35-year-old woman, 5'6" (167.6 cm), 150 lb (68.0 kg). Using the Mifflin-St Jeor formula (the modern gold-standard).

Result: BMR ≈ 1,413 calories/day. This is the energy your body burns at complete rest, just keeping the lights on.

What this means: Multiply by an activity factor to get your TDEE (total daily energy expenditure): 1.2× for sedentary (≈1,696 cal), 1.55× for moderately active (≈2,190 cal), 1.725× for very active (≈2,437 cal). A typical 1 lb/week weight loss needs a daily deficit of 500 calories from TDEE — but never go below your BMR for sustained periods.

Formula & methodology

Formula: Mifflin-St Jeor: men 10w + 6.25h - 5a + 5; women 10w + 6.25h - 5a - 161 (w kg, h cm, a years)

Basal metabolic rate is the energy your body uses at rest to keep organs running. The calculator uses the Mifflin-St Jeor equation, the most accurate common formula, based on weight, height, age, and sex. Multiplying BMR by an activity factor gives TDEE — your maintenance calories. Eat below it to lose weight and above it to gain. BMR is the largest part of daily energy expenditure for most people.

Authoritative source: Mifflin-St Jeor 1990

Frequently asked questions

What is BMR?
Basal metabolic rate — the calories your body burns at complete rest to sustain breathing, circulation, and other basic functions.
How is BMR calculated?
The Mifflin-St Jeor equation uses weight, height, age, and sex. It's considered the most accurate of the common BMR formulas.
What's the difference between BMR and TDEE?
BMR is rest-only energy use; TDEE is BMR multiplied by an activity factor to include movement and exercise.
How do I use BMR to lose weight?
Find your TDEE, then eat in a calorie deficit (commonly 300–500 below TDEE) for gradual, sustainable loss.
Why does BMR fall with age?
Muscle mass tends to decline and metabolism slows with age, so the formula subtracts more calories for older adults.