// Basic Fitness Calculators

BMR Calculator

Calculate the energy your body uses at complete rest, before any activity is counted.

Your details

Your result

Your BMR
1,699kcal/day
  • BMR is the energy you'd burn lying still all day. Add activity (TDEE) for your real daily needs.

Estimates are for general guidance only and are not medical advice. For a personalised plan, book a free guided tour at RPM Gym.

What your result means

Your BMR is the energy cost of staying alive at rest: breathing, circulation, temperature, cell turnover. It's measured in a lab after an overnight fast, lying still and awake — conditions you will never spend a real day in.

That matters because BMR is a floor, not a budget. For most people it accounts for roughly 60–70% of what they spend in a day, with the rest coming from movement, training and digestion. Eating at your BMR isn't eating at maintenance; it is eating well below it.

Its practical use is as a component, not a target. Every calorie tool on this site starts here and multiplies up, so a BMR that looks surprising is worth checking before you trust anything built on top of it.

How it is calculated

Mifflin-St Jeor

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

What it assumes

  • Mifflin-St Jeor was derived in adults and is the equation most commonly recommended for general use over the older Harris-Benedict.
  • It uses total body weight, not lean mass. Where lean mass is known, the Katch-McArdle equation is usually the better estimate.
  • The sex constant (+5 or −161) is a fixed offset from the original regression, not an adjustment applied per individual.
  • Age reduces the estimate linearly at 5 kcal per year, which is a population average rather than a personal trajectory.

Units and rounding

  • Weight in kilograms, height in centimetres, age in years.
  • The result is kilocalories per day, rounded to whole numbers.
  • A zero or negative weight, height or age returns no result rather than a calorie figure.

Worked example

A 28-year-old man, 78 kg, 182 cm.

  1. 10 × 78 = 780
  2. 6.25 × 182 = 1,137.5
  3. 5 × 28 = 140
  4. BMR = 780 + 1,137.5 − 140 + 5 = 1,782.5 kcal/day

About 1,783 kcal/day at complete rest, before a single step, meal or session is counted.

Limitations

  • Two people matched on height, weight, age and sex can differ by several hundred calories in measured resting expenditure. The equation can't see the difference, because it can't see body composition.
  • It reads high for people carrying more fat and low for very lean, muscular people, since muscle is metabolically more expensive per kilogram than fat and total weight treats them alike.
  • It isn't valid for children, and it was not derived in pregnancy, where resting expenditure rises across gestation.
  • Thyroid conditions and some medications change resting metabolism materially. If you have reason to think yours is unusual, this equation can't tell you. Indirect calorimetry can, and a doctor arranges it.
  • A low BMR isn't a diagnosis and not an explanation for weight gain on its own. It's one input among several.

What to do next

  • Don't eat at this number. Multiply it by an activity factor to get a real daily figure. The TDEE calculator does that step and shows the multiplier it used.
  • If you know your body-fat percentage, compare against the Katch-McArdle estimate, which uses lean mass and is generally closer for lean or heavily trained people.
  • Recalculate after a meaningful weight change rather than weekly. A 5 kg change moves BMR by roughly 50 kcal, which is inside the equation's own error.
  • Treat a surprising result as a prompt to check your inputs first. A mistyped height moves this number more than almost anything else.

Sources

Related calculators
TDEEMaintenance CaloriesCalorieLean Body MassBody FatBMI
View all calculators →
// Frequently Asked

Questions, answered.

What is BMR?

Basal metabolic rate: the calories your body uses at complete rest to keep you alive. It's measured lying still and awake after an overnight fast, and it typically accounts for around 60–70% of daily energy use.

What is the difference between BMR and TDEE?

BMR is rest only. TDEE is BMR multiplied by an activity factor to include training, walking, work and digestion. TDEE is always the larger number and it is the one you plan meals around.

Should I eat my BMR to lose weight?

No. Eating at your BMR means eating well below what you actually spend, because it excludes all movement. It's an unnecessarily aggressive deficit for most people and isn't what the number is for.

Which BMR formula is most accurate?

Mifflin-St Jeor is the usual recommendation for general use and is what this calculator implements. If you know your body-fat percentage, Katch-McArdle uses lean mass instead of total weight and tends to be closer for lean or muscular people.

Why is my BMR lower than someone the same weight as me?

Age and sex both shift the equation, and the constants are large: 161 kcal separates the male and female versions. Beyond that, the equation can't distinguish body composition, so real differences between two people of identical weight won't appear here at all.

Does BMR fall as you get older?

The equation subtracts 5 kcal per year of age, and measured resting expenditure does decline across adulthood — partly from ageing itself and partly from the lean mass most people lose along the way. Resistance training addresses the second part.

The resting number is where the plan starts, not where it ends.

The activity half of the equation gets built in the gym. Start it on a free guided tour at RPM Gym in Al Manhal.

Book Free TourWhatsApp Us
Book Free Tour