BMR Calculator: How to Calculate Your Basal Metabolic Rate and Use It for Weight Management

Your Basal Metabolic Rate (BMR) is the number of calories your body burns at rest — just keeping your heart beating, lungs breathing, and cells repairing. It accounts for 60–75% of your total daily energy expenditure, making it the most important number to know for any weight management goal. Without it, you are guessing at how much to eat.

Use the free BMR Calculator to get your personal BMR in seconds based on your age, weight, height, and gender.

The Two Most Accurate BMR Formulas

1. Mifflin-St Jeor Equation (1990)

The most widely recommended formula for the general population:

• Men: BMR = 10 × weight(kg) + 6.25 × height(cm) – 5 × age(years) + 5
• Women: BMR = 10 × weight(kg) + 6.25 × height(cm) – 5 × age(years) – 161

Example: A 35-year-old man, 180 cm tall, 80 kg.
BMR = (10 × 80) + (6.25 × 180) – (5 × 35) + 5
BMR = 800 + 1125 – 175 + 5 = 1,755 cal/day

2. Katch-McArdle Formula

More accurate for athletes and people who know their body fat percentage:

BMR = 370 + (21.6 × Lean Body Mass in kg)

This formula accounts for the fact that muscle burns more calories than fat, even at rest. If you are 70 kg with 15% body fat, your lean mass is 59.5 kg, and your BMR = 370 + (21.6 × 59.5) = 1,655 cal/day.

Katch-McArdle is the better choice if you are lean and muscular; Mifflin-St Jeor is fine for everyone else. The two usually land within 5–10% of each other, so don’t overthink which one you use.

BMR vs TDEE: What’s the Difference?

BMR is just your resting calorie burn. Your Total Daily Energy Expenditure (TDEE) adds activity level:

Activity Level	Multiplier	Example (BMR 1,755)
Sedentary (desk job)	1.2	2,106 cal/day
Light exercise (1–3 days/week)	1.375	2,413 cal/day
Moderate exercise (3–5 days/week)	1.55	2,720 cal/day
Very active (6–7 days/week)	1.725	3,027 cal/day
Extra active (physical job + training)	1.9	3,335 cal/day

Your BMR alone is not your calorie target — you would only eat at BMR if you were bedridden. Always work from TDEE when setting daily calories.

Using BMR for Weight Management

• To lose weight: Eat 300–500 cal/day below your TDEE (≈0.5–1 lb/week loss)
• To maintain weight: Eat at your TDEE level
• To gain muscle: Eat 200–400 cal/day above your TDEE with adequate protein

Why BMR matters more as you age: muscle mass naturally declines about 3–8% per decade after 30, which lowers BMR by roughly 50–100 calories per decade. That is why many people slowly gain weight eating the same amount they did in their 20s. Resistance training preserves muscle and keeps your BMR higher — so pair your calorie target with strength work, not just cardio.

When to Recalculate

• After losing or gaining 10 lb (4–5 kg) — your new weight has a lower (or higher) BMR
• After a major change in activity level (new job, new training program)
• Every few years as you age — BMR naturally drifts downward
• After significant muscle gain — more muscle means a higher BMR

Treat the calculator result as a starting estimate within ±100–200 calories. Track your weight for 2–3 weeks and adjust from real data. Get your exact BMR and TDEE with the BMR Calculator and start making data-driven nutrition decisions today.