BMR Calculator

What does this BMR Calculator do?

Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest just to keep basic functions running — breathing, circulation, cell production. It's typically the largest component of your total daily calorie burn, even before factoring in movement or exercise.

The formula

This calculator uses the Mifflin-St Jeor equation, generally considered more accurate than older formulas like Harris-Benedict:

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

Step-by-step example

For a 28-year-old man, 170 cm tall, weighing 68 kg: BMR = 10×68 + 6.25×170 − 5×28 + 5 = 680 + 1062.5 − 140 + 5 = 1,607.5 kcal/day. That's roughly how many calories his body burns doing absolutely nothing but staying alive for 24 hours.

Tips & common mistakes

• BMR is not the same as your total daily calorie needs — you still need to add calories burned through daily activity and exercise on top of BMR (this calculator shows a couple of activity-adjusted estimates for reference).
• Muscle mass burns more calories at rest than fat mass, so two people of the same weight and height can have meaningfully different actual BMRs — this formula is a population-average estimate, not a lab measurement.
• BMR naturally declines with age, which is one reason calorie needs typically decrease as people get older even at the same activity level.

Why BMR matters even if you're not trying to lose weight

BMR typically accounts for 60–75% of most people's total daily calorie burn, even before counting any deliberate exercise — it's simply the energy cost of staying alive: breathing, circulating blood, maintaining body temperature, and running basic cellular processes. Understanding your BMR is the foundation for any calorie-based goal, whether that's weight loss, weight gain, or simply maintaining your current weight with an accurate calorie target rather than a guess.

Mifflin-St Jeor versus older formulas

Older formulas like Harris-Benedict (from 1919, revised in 1984) are still commonly seen online, but multiple validation studies have found the newer Mifflin-St Jeor equation (1990) to be more accurate for most modern populations, which is why it's the formula this calculator and most contemporary nutrition tools use.

More tips

• BMR naturally decreases with age (roughly 1–2% per decade after young adulthood) largely due to gradual loss of muscle mass — maintaining muscle through resistance exercise is one of the few practical ways to help offset this decline.
• BMR calculators are population-average estimates; for a precise individual measurement, indirect calorimetry (a clinical metabolic test) is the gold standard, though rarely necessary for everyday planning purposes.

Frequently asked questions