BMR Calculator

Your basal metabolic rate is what you burn doing nothing at all. Three equations are printed here in full rather than named and hidden: Mifflin-St Jeor, the 1984 Harris-Benedict revision, and Katch-McArdle, which works off lean mass instead of height and age. The gap between them on your own numbers is the honest width of the estimate.

Sex

Age: 30 years

1580

Height

centimetres

Weight

kilograms

Formula

Mifflin-St Jeor Recommended

Harris-Benedict Katch-McArdle

How this is calculated

Three equations, all of them printed here rather than named and hidden.

Mifflin-St Jeor: 10 × weight in kilograms + 6.25 × height in centimetres − 5 × age, then + 5 for men or − 161 for women. This is the default, because it was the most accurate of the common predictive formulas in the systematic review that compared them.

Harris-Benedict, in the 1984 Roza and Shizgal revision rather than the 1919 original: for men, 88.362 + 13.397 × weight in kilograms + 4.799 × height in centimetres − 5.677 × age; for women, 447.593 + 9.247 × weight + 3.098 × height − 4.330 × age. It tends to read a little higher than Mifflin-St Jeor, and the gap between the two on your own numbers is printed in the comparison table.

Katch-McArdle: 370 + 21.6 × lean body mass in kilograms, where lean mass is your weight less your body-fat percentage. It is the only one of the three that does not ask your age or height, because it does not need them — it works off the tissue that actually burns the calories. That makes it the best of the three if you know your body fat from a scan, and the worst if you are guessing, since an error in the percentage lands straight in the answer.

All three predict a group average from a few measurements. None of them measures you, and the honest way to read the three-way comparison is as the width of the estimate rather than as three candidates for the truth.

Where this comes from

1. A new predictive equation for resting energy expenditure in healthy individuals — Mifflin et al., American Journal of Clinical Nutrition, 1990 (PubMed)
2. The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass — Roza & Shizgal, American Journal of Clinical Nutrition, 1984 (PubMed)
3. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review — Frankenfield et al., Journal of the American Dietetic Association, 2005 (PubMed)

Nothing on this site is medically reviewed — it cites its sources so you can check them. Read our editorial policy. Method last checked 21 August 2026.

Your Basal Metabolic Rate is the starting point for understanding your body's energy needs. It tells you the minimum number of calories required just to keep your body functioning, before any movement or activity is factored in.

For intermittent fasting practitioners, understanding BMR is particularly valuable. It helps you ensure that even on fasting days you are providing your body with enough fuel during eating windows to support essential functions without compromising your metabolic health.

Frequently Asked Questions

What exactly is Basal Metabolic Rate?

BMR is the number of calories your body needs to perform basic life-sustaining functions like breathing, circulating blood, cell production, and maintaining body temperature. It represents the energy you would burn if you stayed in bed all day doing absolutely nothing.

Which BMR formula is the most accurate?

The Mifflin-St Jeor equation, published in 1990, is considered the gold standard by the American Dietetic Association. It tends to be more accurate than the older Harris-Benedict equation, particularly for overweight individuals.

Does intermittent fasting lower your BMR?

Short-term intermittent fasting (up to 48 hours) does not significantly lower BMR and may actually increase it slightly due to norepinephrine release. Prolonged calorie restriction over weeks, however, can lower BMR regardless of whether you practise IF.

How does BMR change with age?

BMR typically decreases by about 1-2% per decade after age 20, primarily due to loss of lean muscle mass. Strength training and maintaining muscle through adequate protein intake can help slow this decline significantly.

Can I increase my BMR naturally?

Yes. Building lean muscle mass through resistance training is the most effective way to raise BMR, since muscle tissue burns more calories at rest than fat tissue. Staying well-hydrated, getting adequate sleep, and eating sufficient protein also support a healthy metabolic rate.

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