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BMR Calculator

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Enter your sex, age, height and weight to estimate basal metabolic rate (BMR) using the Mifflin–St Jeor equation and compare it with a revised Harris–Benedict estimate.

Your details

Sex
years
Estimated BMR (Mifflin–St Jeor)
1,768 kcal/day
Revised Harris–Benedict estimate
1,844 kcal/day

A second formula-based estimate; not a direct measurement.

Difference between estimates
77 kcal/day

Mifflin–St Jeor is 77 kcal/day lower than the revised Harris–Benedict estimate.

Estimate only. This calculator uses height, weight, age and sex to estimate resting energy use. It does not directly measure BMR, account for daily activity, or provide a personal calorie requirement, meal plan or nutrition recommendation.

Results can vary with body composition, health, medication, hormonal factors, sleep, illness, pregnancy or breastfeeding, and other factors. It is intended for adults aged 18 or over. If you are pregnant, breastfeeding, under 18, have an eating disorder, or have a medical condition affecting diet, weight or energy needs, seek advice from a qualified healthcare professional or registered dietitian.

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How to use this calculator

  1. Pick your sex — both formulas use a different constant for men and women.
  2. Enter your age in years.
  3. Enter your height, and pick its unit — centimetres, metres, feet, inches, or feet and inches.
  4. Enter your weight, and pick its unit — kilograms, pounds, or stones and pounds.
  5. Read the estimated BMR from the Mifflin–St Jeor equation, the revised Harris–Benedict estimate, and the difference between the two.

Nothing is submitted anywhere. The calculation runs in the page as you type, and the link in your address bar carries your figures, so it can be shared or bookmarked.

What do I need to enter?

  • Sex — Male or Female. Each formula uses a different constant for each.
  • Age — whole years, from 18 to 120.
  • Height — in centimetres, metres, feet, inches, or feet and inches. Accepted from 130 cm to 220 cm, whichever unit you use.
  • Weight — in kilograms, pounds, or stones and pounds. Accepted from 30 kg to 300 kg, whichever unit you use.

What do the results show?

  • Estimated BMR (Mifflin–St Jeor) — the main figure, in kcal a day at complete rest.
  • Revised Harris–Benedict estimate — the same measure from the older equation, for comparison.
  • Difference between estimates — the gap in kcal a day, with a line saying which equation is higher.

How the estimates are calculated

The calculator converts height to centimetres and weight to kilograms, then applies two published equations that estimate resting energy use. W is weight in kilograms, H is height in centimetres, and A is age in years.

Mifflin–St Jeor, male = 10W + 6.25H − 5A + 5
Mifflin–St Jeor, female = 10W + 6.25H − 5A − 161
Revised Harris–Benedict, male = 88.362 + 13.397W + 4.799H − 5.677A
Revised Harris–Benedict, female = 447.593 + 9.247W + 3.098H − 4.330A
  • Imperial input is converted to kilograms and centimetres first, at full precision.
  • The difference is the absolute gap between the two raw equation outputs, rounded to the nearest whole kcal for display.

Worked example. A 30-year-old, 178 cm, 80 kg male has a Mifflin–St Jeor estimate of 10 × 80 + 6.25 × 178 − 5 × 30 + 5 = 1,768 kcal/day, and a revised Harris–Benedict estimate of about 1,844 kcal/day — so Mifflin–St Jeor is about 77 kcal/day lower.

The equations can produce different values because they are separate population-based prediction models. Neither result is a direct metabolic measurement, and neither accounts for daily activity.

BMR versus activity-adjusted energy use

This calculator compares two resting-energy equations and stops there. It does not apply an activity assumption or estimate average daily energy use.

Want an activity-adjusted estimate? Use the Maintenance Calories Calculator.

Sources

The Mifflin–St Jeor equation comes from Mifflin et al., “A new predictive equation for resting energy expenditure in healthy individuals”, American Journal of Clinical Nutrition, 1990, which gives the male equation as 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) + 5 and reports that the 1919 Harris–Benedict equations overestimated measured resting energy expenditure by about 5%.

Frequently asked questions

What does BMR mean in this calculator?

Basal metabolic rate (BMR) is the energy your body uses at complete rest. Here it is a formula-based estimate from your sex, age, height and weight — the Mifflin–St Jeor equation as the primary estimate, with the revised Harris–Benedict equation (Roza & Shizgal, 1984) shown alongside for comparison. It is not a direct measurement of your metabolism.

Why can the Mifflin–St Jeor and revised Harris–Benedict estimates differ?

They are separate population-based prediction models, fitted to different groups of people at different times. Harris–Benedict dates from 1919 (revised in 1984); Mifflin–St Jeor (1990) is generally considered more accurate for a modern adult population and tends to run a little lower. The two typically agree within about 5%.

Is a formula estimate the same as a direct metabolic measurement?

No. Both equations predict resting energy use from body size and age using population averages. A clinical resting metabolic rate test (indirect calorimetry) measures it directly and can differ from either formula here. Neither result accounts for daily activity.

How is this different from an activity-adjusted maintenance-calorie estimate?

This calculator stops at resting energy use. A maintenance-calorie estimate multiplies a BMR estimate by a broad activity assumption to estimate average daily energy use, which is higher. For that, use the Maintenance Calories Calculator.

Does the estimate depend on sex?

Yes. Both equations use sex-specific constants — Mifflin–St Jeor adds 5 for males and subtracts 161 for females, and Harris–Benedict uses different coefficients throughout. That is why a sex input is required.

Who should seek professional advice before using energy estimates?

This calculator is intended for adults aged 18 or over. If you are pregnant, breastfeeding, under 18, have an eating disorder, or have a medical condition affecting diet, weight or energy needs, seek advice from a qualified healthcare professional or registered dietitian rather than relying on a formula estimate.

Last updated 26 October 2026. Source: Mifflin et al. (1990): A new predictive equation for resting energy expenditure in healthy individuals.