BMR Calculator — Estimate Your Basal Metabolic Rate
Type your age, weight, and height. Get the calories your body burns at complete rest.
What is bmr calculator?
BMR — basal metabolic rate — is the calories your body would burn over 24 hours of complete rest. It’s the largest single component of how much you burn in a day (typically 60–75% of total energy expenditure), which is why it’s the foundation for every other calorie calculation: TDEE applies an activity multiplier on top, calorie-deficit math subtracts a target from TDEE, and macro splits divide that target into protein, carbs, and fat.
The math is the Mifflin-St Jeor 1990 formula:
- Men:
BMR = 10·weight + 6.25·height − 5·age + 5 - Women:
BMR = 10·weight + 6.25·height − 5·age − 161
Weight in kilograms, height in centimeters, age in years. Imperial inputs are converted internally — the formula itself is metric. Mifflin-St Jeor was validated against measured BMR in over 500 adults; the American Dietetic Association recommended it over the older Harris-Benedict equation in 2005, which is why it became the default in clinical practice. Most modern calculators use it; calculators still using Harris-Benedict read about 5% higher for the same inputs.
The formula’s accuracy is statistical — within ±10% of measured BMR for about 70% of adults. Edge cases land further out: very lean athletes (under 12% body fat for men, under 18% for women) often measure above the estimate because Mifflin-St Jeor uses body weight as a proxy for lean mass, and athletes have more lean mass per kg of body weight than the average adult the formula was calibrated against. The opposite is true at the high end of body weight. If you know your lean body mass from DEXA or a reliable scale, the Katch-McArdle formula reads more accurately at the extremes.
Privacy is the final detail worth naming. Every calculation runs locally in your browser. Your inputs are never transmitted. The only state saved is your unit preference (imperial vs. metric) in localStorage, shared across all our fitness tools. Estimates only — not medical advice.
When to use a bmr calculator
- Setting a starting point for a calorie target — Before you can pick a calorie deficit or surplus, you need a maintenance number. BMR is the floor under that number — multiply it by an activity factor and you get TDEE. Most weight-loss plans subtract from TDEE, not BMR, but knowing both keeps the math honest.
- Sanity-checking a 'metabolism is broken' claim — If you suspect your metabolism is unusually low, comparing your measured kcal intake at maintenance against this estimate is a useful first cut. Real BMR varies ±10–15% from the Mifflin-St Jeor estimate, so a 100 kcal/day disagreement is normal — a 500 kcal/day disagreement is worth investigating.
- Programming for athletes vs. dieters — BMR scales with lean body mass, but Mifflin-St Jeor uses total body weight as a proxy. For very lean athletes (under 12% body fat for men, under 18% for women), the estimate reads slightly low; for individuals carrying a lot of body fat, it reads slightly high. Knowing the formula's edge cases helps you adjust your calorie target accordingly.
How to use the BMR Calculator — Estimate Your Basal Metabolic Rate
- Pick your unit system — Toggle between Imperial (lb / ft+in) and Metric (kg / cm) at the top of the form. Your choice is remembered for next time across all our fitness tools.
- Enter your sex, age, weight, and height — Mifflin-St Jeor needs all four. Sex is biological (the formula uses hormonal-baseline metabolic differences, not gender identity). Age, weight, and height accept decimals where they make sense.
- Read your BMR — The headline is calories per day — the energy your body would burn lying still for a full 24 hours. This is the number every other calorie target builds on.
- Multiply by an activity factor for TDEE — BMR alone is not a calorie target — you don't actually lie still all day. Use the linked TDEE calculator to apply the right activity multiplier (1.2 sedentary through 1.9 very active) and get the calories you actually burn day-to-day.
Worked examples
35-year-old man, 180 lb, 5'10"
Input: Sex Male, Age 35, Weight 180 lb, Height 5'10"
Output: BMR ≈ 1,758 kcal/dayA typical resting energy budget for an average-build adult man. Multiply by an activity factor of 1.55 (moderate) → about 2,724 kcal/day TDEE.
30-year-old woman, 65 kg, 165 cm
Input: Sex Female, Age 30, Weight 65 kg, Height 165 cm
Output: BMR ≈ 1,370 kcal/dayThe Mifflin-St Jeor sex constant differs by 166 kcal/day — that's the gap you'd see between the same lifter calculated as male vs. female.
65-year-old woman, 60 kg, 160 cm
Input: Sex Female, Age 65, Weight 60 kg, Height 160 cm
Output: BMR ≈ 1,114 kcal/dayBMR drops about 5 kcal/year of age in the formula — at 65 vs 30, the same body burns 175 kcal/day less at rest.
Frequently asked questions
What is BMR?
Which formula does this calculator use?
How accurate is the estimate?
Why does muscle mass not appear in the formula?
BMR = 370 + 21.6 × lean kg. For most adults the difference between the two formulas is under 100 kcal/day.Should I eat at BMR for weight loss?
Does BMR change throughout life?
−5 × age term — a 30-year-old burns 175 kcal/day more at rest than a 65-year-old, all else equal. Resistance training preserves the muscle that drives BMR, which is why strength work is consistently associated with better metabolic outcomes in older adults.Why is the result lower if I select female?
Are my numbers stored or sent anywhere?
localStorage, so the toggle remembers your choice across visits and across our other fitness tools. Estimates only — not medical advice. Consult a registered dietitian or your doctor before starting a calorie deficit, especially if you're pregnant, nursing, under 18, or have a medical condition.