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BMR Calculator | Estimate Basal Metabolic Rate

Find the calories your body burns at complete rest using the Mifflin-St Jeor equation, then multiply by your activity level for your daily maintenance target. The foundation of every weight-loss and muscle-gain plan — enter your details and get your BMR and TDEE.

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

Results

Enter values above and click Calculate to see your result instantly.

Quick reference

Activity multipliers (BMR x factor = maintenance calories):

Activity level	Multiplier
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:

Term	Meaning
BMR	Calories burned at complete rest
TDEE	BMR x activity factor
Deficit	Eat below TDEE to lose weight
Surplus	Eat 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)

The BMR Calculator is built on a well-established calculation method. It uses the formula Mifflin-St Jeor: men 10w + 6.25h - 5a + 5; women 10w + 6.25h - 5a - 161 (w kg, h cm, a years) to turn your inputs into a reliable result. 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 The steps are shown on the page so you can follow the reasoning from input to output.

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.

What is the BMR Calculator?

The BMR Calculator is a free, browser-based health calculator tool that helps you. 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-. Instead of working through the math by hand or in a spreadsheet, you enter your values and the calculator returns an accurate result instantly — while still showing the formula and the steps so you can verify the reasoning. It is designed for quick everyday use: no sign-up, no installation, and everything runs locally in your browser for complete privacy.

How to use the BMR Calculator

Enter the required values into the input fields.
Press the calculate button — the result appears immediately, updated live as you change any value.
Read the step-by-step breakdown below the result to see exactly how the calculation was performed.
Use the interpretation guide to understand what the result means for your situation, and try different inputs to see how they change the outcome.

How to use the BMR Calculator

Enter your age, sex, height, and weight, then press calculate. The tool applies the Mifflin-St Jeor equation — for men, BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5; for women, the same with − 161 — and returns your basal metabolic rate in calories per day. This is the energy your body burns at complete rest, before any activity, and it typically accounts for 60–70% of your total daily expenditure.

Interpreting your result

Your BMR is the floor of your calorie needs: eating below it for extended periods is neither sustainable nor healthy. Multiply your BMR by an activity factor (about 1.2 for sedentary up to 1.9 for very active) to estimate your total daily energy expenditure (TDEE), then set your calorie target relative to that — a 300–500 calorie deficit for steady fat loss or a surplus for muscle gain. Because BMR falls roughly 1–2% per decade after age 30, mostly from muscle loss, the number you get today will not be the number you need in ten years.

Common mistakes to avoid

The most common error is treating BMR as the number of calories you can eat — it is not; your daily maintenance is higher once activity is included. Second, using imperial units without conversion — the equation requires kilograms and centimetres, and the tool converts automatically. Third, relying on the result for medical decisions: BMR equations are population estimates with roughly ±200 calorie individual variation, so treat the number as a starting point, not a prescription. Finally, updating weight and age as they change — stale inputs produce stale targets.

Tips for best results

Weigh yourself in the morning before eating for the most consistent input. Recalculate whenever your weight changes by more than 5 kg or your activity level shifts. Pair the BMR with the activity multiplier to get TDEE, then adjust your intake by 300–500 calories toward your goal rather than making extreme cuts. If you lift weights, your BMR estimate may understate your needs — muscle burns more at rest than fat. Track your weight for 2–3 weeks and adjust intake by what the scale actually does.

Authoritative source: Mifflin-St Jeor 1990

Frequently asked questions

What is BMR?

The BMR Calculator is free, private, and accurate: it runs entirely in your browser (no uploads, no accounts), applies the standard calculation, and explains each step so you can verify the result. 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 There is no limit on usage, and it works on any device.

How is BMR calculated?

The Mifflin-St Jeor equation estimates it from age, sex, height, and weight: for men, BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5; for women, the same with − 161. It was developed in 1990 and is the most accurate general-purpose equation. The result is the calories burned at complete rest, before activity, and it feeds the TDEE estimate via the activity multiplier.

What's the difference between BMR and TDEE?

BMR is the energy your body burns at complete rest — breathing, circulation, and cell maintenance — typically 60–70% of your daily burn. TDEE adds the rest: physical activity, exercise, and the thermic effect of food. TDEE = BMR × activity multiplier, with multipliers from about 1.2 (sedentary) to 1.9 (very active). Your maintenance calories are TDEE, not BMR.

How do I use BMR to lose weight?

Enter the required values into the input fields and press the calculate button. The tool applies the formula Mifflin-St Jeor: men 10w + 6.25h - 5a + 5; women 10w + 6.25h - 5a - 161 (w kg, h cm, a years) and returns the result with a short explanation of each step, so you can check the working yourself.

Why does BMR fall with age?

BMR declines roughly 1–2% per decade after age 30, mainly because of declining muscle mass — muscle burns more calories at rest than fat, and age-related muscle loss lowers the resting burn. The Mifflin-St Jeor equation captures this with the age term. Strength training slows the decline by preserving muscle, which is why resistance exercise is the best counter.

What does the BMR Calculator do?

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. The calculator takes your inputs, applies the standard calculation, and returns a clear result so you can make an informed decision without doing the math by hand.

What formula does the BMR Calculator use?

The BMR Calculator applies the standard formula: Mifflin-St Jeor: men 10w + 6.25h - 5a + 5; women 10w + 6.25h - 5a - 161 (w kg, h cm, a years). The tool walks through each step of the calculation so you can verify the numbers yourself.

Is the BMR Calculator free and private?

Yes — the BMR Calculator. There is no sign-up, no paywall, no trial, and no limit on how many calculations you can run. CalcaTools covers its costs with non-intrusive display advertising, so the calculator itself never asks for payment or restricts any feature.

How accurate is the BMR Calculator?

The BMR Calculator applies the standard formula: Mifflin-St Jeor: men 10w + 6.25h - 5a + 5; women 10w + 6.25h - 5a - 161 (w kg, h cm, a years). It is tested against published worked examples before launch and uses native double-precision arithmetic, so results are accurate to typical precision for the values you enter — with no intermediate rounding that could distort the answer.

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