Skip to content
Calybite
App Store

Free tool

BMR calculator

Your basal metabolic rate is what you would burn lying still in a warm room all day, having eaten nothing — the cost of running a heart, a brain, a liver and a set of kidneys. For most adults it accounts for around 60 to 70 percent of total daily energy use.

Written by the Calybite team · Last updated 25 August 2026

Your BMR

1,370 kcal

What your body burns at complete rest, before any movement.

BMR (at rest)

1,370 kcal

TDEE (maintenance)

2,123 kcal

BMI (context only)

23.8 · Healthy weight

Estimates for generally healthy adults, using Mifflin-St Jeor. Real expenditure varies by roughly ±10% between people of identical size. Not medical advice — if you have a medical condition, are pregnant, or are recovering from an eating disorder, talk to a professional before using a calorie target.

Your BMR sets the floor. Calybite tracks what you put back on top of it.

Log a meal in four seconds and see it against your numbers.

Point the camera at the plate. Calybite names it, counts it, and holds it against the target above.

The equation, in full

This calculator uses Mifflin-St Jeor, published in 1990 and still the default in most clinical settings because it outperformed the older Harris-Benedict equation on modern populations:

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

Worked through for a 40-year-old man, 5′10″ (178 cm), 181 lb (82 kg):

BMR = 10(82) + 6.25(178) − 5(40) + 5
    = 820 + 1,112.5 − 200 + 5
    = 1,737 kcal/day

Notice what the equation contains and what it does not. Weight carries the most influence, height and age adjust it, and the sex term is a blunt 166-calorie constant standing in for average differences in body composition. There is no input for muscle mass, because the equation was built to work without a body-composition scan.

BMR is not your calorie target. Eating at your BMR means eating as though you spent the entire day motionless. Almost nobody should do that. To get a number you can actually eat to, multiply by an activity factor — which is exactly what find your maintenance calories does.

Where the estimate goes astray

Predictive equations land within about ten percent of measured resting expenditure for most healthy adults, which is good enough to plan from and not good enough to argue with. They are least reliable at the extremes: the very muscular, the very lean, the very heavy, the elderly, and anyone with a thyroid condition or on medication that affects metabolism.

Muscle mass is the most common source of a bad fit. Two people at 82 kg with different amounts of lean tissue have genuinely different resting rates, and the equation cannot tell them apart because it never asked. If you carry noticeably more or less muscle than average for your size, expect the estimate to sit low or high respectively.

Why anyone needs this number

On its own, rarely. BMR is a building block: it is the input to TDEE, which is the input to a deficit or surplus, which is the thing you actually eat. It is worth calculating mostly so the later numbers stop feeling arbitrary — when you can see that roughly two-thirds of your daily calories are spent before you get out of bed, the size of a 500-calorie deficit stops seeming trivial.

Once you have it, split your calories into macros or read how to read your calorie number.

Sources

Keep going

Protein calculator

Grams of protein a day, and why the RDA is a floor not a goal.

How many calories should I eat?

What the number means, where it comes from, and where it goes wrong.

kcal to cal converter

Convert kcal, calories, food Calories, kilojoules and joules.

Back to all calculators.

Stop doing the arithmetic.

A calculator gives you the target once. Calybite holds every meal against it — no credit card, no payment gateway, and free meal scans every day.

App Store