A walkthrough, end to end.
- 1
Pick metric or imperial. Your inputs swap automatically — feet/inches/pounds for imperial, centimeters/kilograms for metric.
- 2
Enter your height, weight, age and sex. All four are required for BMR — unlike BMI, the formula genuinely uses each variable. Sex is required because men typically have more lean mass at the same body size.
- 3
Read your BMR. It's the number of calories your body burns over 24 hours doing nothing — keeping your heart pumping, lungs breathing, brain running, organs maintaining temperature.
- 4
Compare two formulas. We show Mifflin–St Jeor (the modern standard) and Harris–Benedict (1984 revision) side by side. They usually agree within 5%; pick Mifflin if you want one number.
Mifflin–St Jeor formula
The Mifflin–St Jeor equation, published in 1990, is the most accurate of the published BMR formulas for the general adult population. It estimates resting energy expenditure from height, weight, age and a sex constant.
What you can do with this.
BMR calculator for men
For men, the sex constant is +5. A 30-year-old man at 5'10" (178 cm) and 80 kg has a BMR of roughly 1,800 kcal — that's the energy his body burns lying still in bed for 24 hours.
BMR calculator for women
For women, the sex constant is −161 (women carry slightly more body fat at the same body size on average, which is metabolically less active than muscle). A 30-year-old woman at 5'5" (165 cm) and 65 kg has a BMR of roughly 1,400 kcal.
BMR for weight loss
Don't eat below your BMR for sustained periods. The metabolic adaptation that follows aggressive cuts undermines long-term loss and is hard to reverse. Calculate your TDEE (BMR + activity) and create a modest deficit from there.
Mifflin–St Jeor vs Harris–Benedict
Harris–Benedict (1919, revised 1984) is the older standard. Mifflin–St Jeor (1990) is more accurate against modern populations and what professional dietitians use today. Both are shown above for comparison; values usually agree within 5%.
BMR for athletes and lifters
Mifflin–St Jeor underestimates BMR for very lean, muscular people because it doesn't use body composition. If you know your body fat percentage, the Katch–McArdle formula (based on lean body mass) is more accurate — but for most people, Mifflin is close enough.
BMR vs RMR — what's the difference?
BMR (basal metabolic rate) is measured under strict lab conditions: post-overnight fast, awake, lying still, neutral temperature. RMR (resting metabolic rate) drops the strict prep — same idea, slightly higher number. Casual usage treats them as interchangeable; this calculator returns BMR.
BMR calculator 2026 — what's current
The Mifflin–St Jeor equation hasn't changed for 2026 — it's still the most accurate published BMR formula for general adult populations. What has evolved is the framing: BMR is now widely understood as a starting point for TDEE, not a target intake. This calculator reflects 2026 best practice by surfacing both Mifflin and the comparison Harris–Benedict number plus the next-step TDEE link.
Frequently asked.
Mifflin–St Jeor (1990) — it's what the Academy of Nutrition and Dietetics recommends. Harris–Benedict's 1984 revision is also commonly cited. For people with known body fat percentage, Katch–McArdle is more precise.
Sex changes the formula's constant by 166 kcal (men +5, women −161). This reflects real biological differences in average body composition — men carry more lean mass per kg of body weight on average, and lean mass is metabolically more active than fat.
No — your BMR is what you'd burn at complete rest. Your real daily burn (TDEE) includes movement and digestion, and is 1.2× to 1.9× your BMR depending on activity. Eat at TDEE to maintain weight, slightly below to lose, slightly above to gain.
Casually, yes. Strictly, BMR is measured under controlled lab conditions (post-overnight fast, awake, supine, neutral temperature); RMR drops some of that prep. RMR is typically 5-10% higher. This calculator returns BMR using Mifflin–St Jeor.
Yes — it slowly declines, typically 1–2% per decade after age 30. The formula accounts for this by subtracting 5 kcal per year of age. Strength training and maintaining lean mass slow the decline.
No. Every calculation runs in your browser. There is no server-side processing, no analytics on inputs, and no cookies storing what you typed.