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BMR Calculator (Basal Metabolic Rate)
Basal metabolic rate by the Mifflin-St Jeor, Harris-Benedict and Katch-McArdle equations, with calories for each activity level.
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Your basal metabolic rate (BMR) is the number of calories your body burns at complete rest – just to breathe, pump blood, keep warm and run your organs. This BMR calculator works it out with the three most widely used equations, Mifflin-St Jeor, Harris-Benedict and Katch-McArdle, and multiplies it by your activity level to show how many calories you burn in a day.
How to Use the BMR Calculator
- Enter your age and sex.
- Enter your height and weight in US or metric units.
- If you know your body fat percentage – from a DEXA scan, smart scale or calipers – enter it to get the Katch-McArdle result too.
BMR Formulas
Mifflin-St Jeor (1990) – the most accurate for most adults:
- Men: 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5
- Women: 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161
Harris-Benedict (revised 1984):
- Men: 88.362 + 13.397 × kg + 4.799 × cm − 5.677 × age
- Women: 447.593 + 9.247 × kg + 3.098 × cm − 4.330 × age
Katch-McArdle: 370 + 21.6 × lean body mass (kg). It uses lean mass rather than weight, so it suits lean, muscular people who know their body fat.
Example
A 35-year-old man, 5 ft 9 in (175.3 cm) and 170 lb (77.1 kg): Mifflin-St Jeor gives 10 × 77.1 + 6.25 × 175.3 − 5 × 35 + 5 = about 1,696 calories a day. Harris-Benedict gives about 1,764. A 40-year-old woman, 5 ft 4 in and 150 lb, has a BMR of about 1,335.
From BMR to Daily Calories
BMR is only part of what you burn. Multiply it by an activity factor to get your total daily energy expenditure (TDEE):
| Activity level | Multiply BMR by |
|---|---|
| Sedentary (desk job, little exercise) | 1.2 |
| Lightly active (exercise 1–3 days a week) | 1.375 |
| Moderately active (3–5 days a week) | 1.55 |
| Very active (6–7 days a week) | 1.725 |
| Extra active (physical job or twice-a-day training) | 1.9 |
Eating fewer calories than your BMR for long periods isn't recommended; it makes it hard to get enough nutrients. For a full breakdown use the TDEE calculator, and to plan weight loss, the calorie deficit calculator.
What Affects Your BMR?
- Muscle mass: muscle burns more at rest than fat, which is why strength training helps.
- Age: BMR falls slowly with age, largely because of muscle loss.
- Sex and size: larger bodies and men, on average, have higher BMRs.
- Health: thyroid conditions, some medications and pregnancy change BMR. Equations can be off by 10% or more for an individual.
Sources
- Mifflin MD, St Jeor ST et al. – A new predictive equation for resting energy expenditure (Am J Clin Nutr, 1990)
- Roza AM, Shizgal HM – The Harris Benedict equation reevaluated (Am J Clin Nutr, 1984)
- NIH NIDDK – Body Weight Planner
Last reviewed: October 2026 by the ShrinkBee team. Estimates for healthy adults; this page is not medical advice.
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