BMR Calculator

What is basal metabolic rate?

Basal metabolic rate is the calories your body burns at complete rest to stay alive — breathing, circulation, cell repair, body heat. It’s typically 60–75% of your total daily burn, and it’s the foundation every calorie target is built from.

How this calculator works

• Runs your numbers through Mifflin-St Jeor, the equation most clinical guidelines recommend for estimating resting metabolic rate.
• Offers the revised Harris-Benedict formula as an alternative, or averages the two if you’d rather not choose.
• Also reports sedentary maintenance — BMR × 1.2 — your burn on a day with little or no movement.
• Handles imperial and metric inputs, so there’s no unit math on your side.

How to use the result

1. Treat the BMR figure as a floor, not a target. It’s what you’d burn lying in bed all day — eating at or below it is too aggressive for almost anyone.
2. Multiply by an activity factor — 1.2 for sedentary up to about 1.9 for very active — to get your total daily energy. That maintenance number, not BMR, is what predicts weight change.
3. Set the goal from maintenance: roughly 500 kcal below for fat loss, 200–300 above for lean gain. And don’t drop under ~1,200 kcal (women) or ~1,500 (men) without a doctor in the loop.
4. If you’re logging food, splitting those calories into macros is the natural next step — set protein first, since it protects muscle in a deficit.
5. Recalculate after every 5–10 lbs of change. A lighter body costs less to run, so the estimate drifts as you progress.

What’s the difference between a BMR calculator and an RMR calculator?

Almost none in practice. Strictly, basal metabolic rate is measured under rigid lab conditions — fasted, fully rested, warm room — while resting metabolic rate is measured under everyday conditions and usually runs slightly higher. Prediction equations can’t tell the difference: both are estimated from the same age, sex, and body-size inputs, so a BMR calculator and an RMR calculator return nearly identical numbers. For meal planning, treat them as the same thing.

Common mistakes

• Eating at your BMR. It excludes every step, workout, and fidget — a deficit that size stalls most people within weeks.
• Treating the estimate as exact. Real values vary ±10–15%, and the equations can’t see body composition — two people at the same weight can burn hundreds of calories apart.
• Debating formulas. The gap between Mifflin-St Jeor and Harris-Benedict is small next to normal day-to-day noise; picking one and staying consistent beats chasing precision.
• Applying it to children. These equations are calibrated for adults and older teens — growing kids burn differently, and the math here doesn’t apply under age 15.
• Assuming metabolism is fixed. Prolonged dieting, poor sleep, illness, and some medications all shift real burn — if the scale ignores the math for three weeks, adjust the number, not your effort.

BMR tells you what your body costs to run at idle — whether you should cut, hold, or gain is a separate decision. If you’re unsure which direction, a body mass index check is a sensible place to start.