CalcNest

BMR Calculator

Your basal metabolic rate is the energy your body uses just to stay alive — breathing, circulation, cell repair — before any movement at all. It typically accounts for 60–70% of all calories you burn. This calculator computes it with the two best-known equations so you can compare.

The two equations

Mifflin-St Jeor (1990):  10×kg + 6.25×cm − 5×age + 5 (men) / − 161 (women)
Harris-Benedict (revised 1984):  88.362 + 13.397×kg + 4.799×cm − 5.677×age (men)

Mifflin-St Jeor is the modern default — validation studies find it lands within 10% of measured BMR for more people than any other formula. Harris-Benedict, dating to 1919 and revised in 1984, tends to read 5% or so higher; we show it for comparison because many older charts and apps still use it.

From BMR to daily calories

BMR is not the number to eat — it's the floor of your energy budget. Multiply it by an activity factor to get your true daily burn (TDEE): ×1.2 if sedentary, ×1.375 lightly active, ×1.55 moderately active, ×1.725 very active. Our calorie calculator does this and adds goal-based targets.

What changes your BMR

  • Muscle mass — each kg of muscle burns roughly 10–15 kcal/day at rest versus ~4 for fat, which is why resistance training nudges metabolism up.
  • Age — BMR declines gradually, mostly because muscle declines; training blunts much of the drop.
  • Dieting — prolonged large deficits can suppress BMR by 5–15% (adaptive thermogenesis), one reason crash diets stall.
  • Thyroid status, genetics, and body size account for most of the rest.

This tool provides general estimates for educational purposes and is not medical advice. Consult a healthcare professional for guidance specific to you.

Frequently asked questions

What exactly does BMR include?

Only life-support at complete rest: heartbeat, breathing, brain activity, temperature regulation, and cell turnover. It excludes digestion (~10% of intake) and all movement, from typing to workouts.

Should I eat at my BMR to lose weight?

That's more aggressive than it sounds — your real daily burn is BMR × 1.2 or more, so eating at BMR builds in a 20%+ deficit automatically. It works for some, but a target set slightly below TDEE is easier to sustain and preserves more muscle.

Why do Mifflin and Harris-Benedict disagree?

They were fitted on different populations in different eras. Harris-Benedict's 1919 sample was small and leaner-era; Mifflin's 1990 sample better matches modern bodies, which is why dietetic associations recommend it.

Can I increase my BMR?

Meaningfully, yes — build muscle. A few kilograms of added muscle raises resting burn modestly and raises training burn a lot. Sleep, adequate protein, and not chronically under-eating also keep BMR from adaptive suppression.

Is a higher or lower BMR better?

Neither is 'better' — it's just your body's idle fuel consumption. What matters is knowing it, so you can set calorie targets that match your goal instead of guessing.