Which BMR formula is most accurate?

Mifflin–St Jeor (1990) is the most accurate general-population formula, outperforming the older Harris–Benedict equation by about 5% on average. Katch–McArdle is slightly more accurate if you know your lean body mass, but requires a body-fat measurement. For most users, Mifflin–St Jeor is the right default.

Why does BMR decrease with age?

Two main reasons. First, muscle mass naturally declines from about age 30 onward (sarcopenia), and muscle has a higher metabolic rate than fat. Second, organ function efficiency drops modestly with age. Strength training and adequate protein can slow this decline significantly — a 60-year-old who lifts weights may keep nearly the same BMR as at 30.

Does BMR differ between men and women?

Yes. Men typically have higher BMR than women of the same weight and height because men carry more lean body mass and have higher testosterone levels supporting muscle tissue. The Mifflin–St Jeor formula bakes this in with a different constant term (+5 for men, −161 for women).

Can BMR be measured directly?

Yes — indirect calorimetry (measuring your oxygen consumption and CO₂ production in a lab) is the gold standard. It is accurate but expensive and rarely necessary. Formula estimates like Mifflin–St Jeor are within ±10% of direct measurement for most people and are perfectly sufficient for weight-management planning.

How can I increase my BMR?

Build more lean muscle through strength training (each additional kilogram of muscle adds roughly 13 kcal/day to BMR), eat adequate protein (supports muscle), stay well-hydrated, get sufficient sleep, and avoid extreme calorie restriction (which triggers adaptive thermogenesis and lowers BMR). Small, consistent efforts compound over years.

Will eating at BMR cause weight loss?

Yes, in the short term — you would be in a severe calorie deficit because any physical activity adds to calories burned beyond BMR. However, eating at or below BMR for extended periods is not recommended: it causes muscle loss, fatigue, hormonal disruption, and metabolic slowdown. Aim for 500 kcal below TDEE, not below BMR.

Does BMR change day to day?

Yes, slightly — it shifts with stress, illness, sleep quality, ambient temperature, and hormonal cycles. Day-to-day variation is small (a few percent) and averages out across a week. Use your calculated BMR as a stable weekly baseline rather than a rigid daily target.

BMR Calculator

Health

Calculate your Basal Metabolic Rate — calories burned at rest.

Health

BMR Calculator

Generated on April 24, 2026

Age (years)

Weight

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?What is the BMR Calculator?

Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest to maintain basic life-sustaining functions — breathing, circulation, cell repair, temperature regulation, and organ function. It represents 60–75% of your total daily calorie expenditure, making it the foundation of any weight-management or performance-nutrition plan. Knowing your BMR allows you to build accurate calorie goals — whether for fat loss, muscle gain, or maintenance — rather than relying on generic recommendations that do not account for your weight, height, age, and sex.

The Formula

Mifflin–St Jeor equation. Men: BMR = 10W + 6.25H − 5A + 5. Women: BMR = 10W + 6.25H − 5A − 161. (W = weight in kg, H = height in cm, A = age in years)

The Mifflin–St Jeor equation, published in 1990, is considered the most accurate predictive BMR formula for the general population and is preferred by dietitians worldwide. Weight contributes most (heavier bodies need more baseline energy to sustain); height is secondary (taller people have more surface area and slightly higher BMR); age is inverse (BMR declines with age as muscle mass decreases and organ function slows); sex matters because men typically carry more lean mass, which has a higher metabolic demand than fat tissue.

Practical Examples

A 30-year-old male weighing 75 kg at 178 cm has a BMR of approximately 1,688 kcal/day — his body burns that much just resting.

A 28-year-old female at 60 kg and 165 cm has a BMR around 1,361 kcal/day — notably lower due to sex and lower body mass.

A 50-year-old male at 85 kg and 180 cm has a BMR near 1,730 kcal/day — slightly lower than his 30-year-old self at the same weight.

A 25-year-old female athlete at 55 kg and 170 cm has a BMR of about 1,343 kcal/day, consistent with her lean frame.

As a 40-year-old loses muscle and gains fat over the next decade, his BMR can fall by 100–200 kcal/day — a main reason 'middle-age spread' is so common.

Someone shifting from 70 to 80 kg adds roughly 100 kcal/day to their BMR just from needing to maintain the extra tissue.

Frequently Asked Questions

BMR is your calorie burn at rest — only the energy needed to keep vital functions running. TDEE (Total Daily Energy Expenditure) is BMR multiplied by an activity multiplier, adding the calories you burn through planned exercise, general daily movement, and the thermic effect of food. Use BMR as the base, TDEE as the target for diet planning.

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BMR Calculator

BMR Calculator

?What is the BMR Calculator?

The Formula

Practical Examples

Frequently Asked Questions

What is the difference between BMR and TDEE?

Which BMR formula is most accurate?

Why does BMR decrease with age?

Does BMR differ between men and women?

Can BMR be measured directly?

How can I increase my BMR?

Will eating at BMR cause weight loss?

Does BMR change day to day?

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