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BMR calculator

How many calories your body burns at rest. We use the Mifflin–St Jeor equation — the most accurate of the common BMR formulas for modern adults — and add a TDEE estimate based on your activity level.

Your result

1,735 kcal/day BMR

You burn about 2,689 kcal/day at your current activity level (TDEE).

What to do with this: For weight maintenance, eat roughly your TDEE. For fat loss, aim ~20% below TDEE. For muscle gain, ~10% above. Pair with our macro calculator to split that into protein, fat, and carbs.

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What is BMR?

Your basal metabolic rate (BMR) is the number of calories your body burns at complete rest to keep core processes running: breathing, circulation, brain function, cellular repair. It typically accounts for 60–75% of total daily energy expenditure for sedentary people, and a smaller share for active people. BMR isn't a license to eat that much — it's the floor before any movement is added.

Why Mifflin–St Jeor?

The two equations you'll see online are Harris–Benedict (1919, revised 1984) and Mifflin–St Jeor (1990). Validation studies have repeatedly found Mifflin–St Jeor more accurate in modern populations, particularly in non-obese adults — Frankenfield et al., J Am Diet Assoc 2005, found it accurate within ±10% of measured BMR in 82% of non-obese subjects, beating four other equations. The formula:

BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age(years) + s where s = +5 for men, −161 for women

From BMR to TDEE

BMR × an activity multiplier gives Total Daily Energy Expenditure (TDEE) — what you burn in a typical day. We use the Roza & Shizgal (1984) modifiers:

  • Sedentary (1.2) — desk job, little/no exercise.
  • Light (1.375) — light exercise 1–3 days/week.
  • Moderate (1.55) — moderate exercise 3–5 days/week.
  • Very active (1.725) — hard exercise 6–7 days/week.
  • Athlete (1.9) — physical job or 2×/day training.

How to use this number

  • Maintenance: eat ≈ TDEE.
  • Fat loss: aim ~15–25% below TDEE. Larger deficits work short-term but cost lean mass and adherence.
  • Muscle gain: ~5–15% above TDEE plus a structured training program.

Reassess every 4–6 weeks. Real-world expenditure drifts as you lose or gain weight and as activity patterns change. The number is a starting point, not a verdict.

References

  • Mifflin MD et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241-247.
  • Frankenfield D et al. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults. J Am Diet Assoc. 2005;105(5):775-789.
  • Roza AM, Shizgal HM. The Harris Benedict equation reevaluated. Am J Clin Nutr. 1984;40(1):168-182.