BMR Calculator

Your BMR (Basal Metabolic Rate) is the energy your body burns at complete rest — keeping your heart beating, lungs working and cells repairing. It's typically 60–75% of your daily calorie burn, before any activity. It is also the single biggest driver of how much you can eat without gaining weight, which is why it is the foundation of nearly every calorie-based plan.

What actually drives your BMR

Your resting burn is largely set by your lean body mass — muscle, organs and bone all consume energy even at rest, while fat tissue needs very little. That explains the two most common observations: men tend to have a higher BMR than women of the same size (more muscle on average), and BMR slowly declines with age (as lean mass tends to drop) unless it is preserved through strength training. This is also why two people of identical height and weight can have quite different BMRs.

Mifflin-St Jeor

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

For a 30-year-old man, 175 cm, 75 kg:

BMR = 750 + 1093.75 − 150 + 5 ≈ 1,699 kcal

This formula was published in 1990 as an update to older equations that had drifted out of step with modern populations — several studies found it estimated resting energy expenditure more accurately than its predecessors for many adults. It remains one of the most widely recommended daily-energy equations.

Katch-McArdle

BMR = 370 + 21.6 × lean body mass (kg)

Lean mass = weight × (1 − body fat %). If you know your body fat percentage, this formula is often more accurate, especially for athletes — muscle burns more calories at rest than fat. Its weakness is obvious from the equation: it is only as good as your body-fat measurement. If that number is off, so is the BMR, so the Mifflin-St Jeor estimate is often a safer default when you are unsure of your body composition.

From BMR to your real needs

BMR is not your target calories — it's the baseline. Multiply by an activity factor to get your TDEE:

So a BMR of 1,699 with moderate activity → ~2,633 kcal/day to maintain weight. See the Maintenance Calories Calculator for the full picture.

Reading your BMR wisely

BMR formulas are population-derived estimates, accurate to maybe a few hundred calories per day for a given individual, not precise personal measurements. They also assume healthy thyroid and hormonal function — a sluggish thyroid can lower resting burn substantially. Rather than treating the number as gospel, use it as a starting point and adjust based on how your weight actually responds over a couple of weeks. This content is for general education and is not medical advice.