BMR Calculator
Calculate Basal Metabolic Rate (BMR)
BMR Calculator tool
BMR Calculator
BMR Calculator: key facts
- What it does
- Calculate Basal Metabolic Rate (BMR)
- Category
- Health & Fitness Calculators
- Cost
- Free, with no account, sign-up, or install.
- Your data
- Runs entirely in your browser — the files and text you enter are never uploaded to a server.
- Last reviewed
- . Report an incorrect result.
What the BMR Calculator does
Your basal metabolic rate is the number of calories your body burns at complete rest just to keep you alive — breathing, circulating blood, maintaining temperature. This calculator estimates it using the Mifflin-St Jeor equation, the modern standard, from your sex, age, weight, and height.
BMR is the starting point for any calorie plan: it is the floor below which you should rarely eat, and the base that activity is added to in order to find your full daily needs. Anyone setting a weight-loss, maintenance, or muscle-gain target uses it as the anchor number before factoring in exercise.
Using the BMR Calculator, step by step
- Select your sex.
- Enter your age in years.
- Enter your weight in kilograms.
- Enter your height in centimeters.
- Read your BMR in calories per day, then carry it into a TDEE calculator to factor in activity.
Mifflin–St Jeor, and why this equation
Basal metabolic rate is the energy your body spends doing nothing at all — maintaining temperature, circulation, breathing, and cell repair while completely at rest. For most people it accounts for the largest share of daily energy use, which is why it is the starting point for any calorie target.
This calculator uses the Mifflin–St Jeor equation, published in 1990. It is preferred here over the older Harris–Benedict formula because validation studies since have generally found it more accurate for contemporary populations. The two share a structure — weight, height, and age each contribute a linear term — and differ in their coefficients and in the constant applied by sex.
Note that the sex term is a single constant: +5 or −161. Everything else in the equation is identical, so the same body measurements produce figures 166 kcal apart.
- The default entry — 70 kg, 175 cm, 25 years, male — gives 1,673.75 kcal a day.
- The same measurements with the female constant give 1,507.75 kcal.
- Age alone costs 5 kcal a year on this equation, so the same body at 55 rather than 25 comes out 150 kcal lower.
What makes this one worth using
- It uses the Mifflin-St Jeor equation, which research has found more accurate for most people than the older Harris-Benedict formula.
- It asks only for the four inputs the equation actually needs — sex, age, weight, height — keeping it fast and free of guesswork.
- The result is a clean daily calorie figure ready to feed into activity and goal calculations.
- It calculates locally and instantly, so your body metrics never leave your device.
What BMR is not, and how much it varies
BMR is not the number of calories to eat. It is what you would burn lying still all day, so eating at BMR while living a normal life means a substantial deficit. To get a usable daily figure you multiply BMR by an activity factor, which is what a TDEE calculation does.
The equation is a population regression, which means it describes an average and individuals scatter around it. Genuine measured resting metabolic rate can differ from a predicted figure by ten to fifteen percent in either direction, because body composition, thyroid function, medication, and recent dieting history all move it and none of them appear as inputs here. Muscle is more metabolically active than fat, so two people of identical weight, height, age and sex can have meaningfully different real rates.
Use the output as a starting estimate to be adjusted against what actually happens over a few weeks, and treat any calorie target for weight change — particularly a large deficit, or anything undertaken alongside a medical condition — as a subject for a doctor or a registered dietitian rather than a calculator.
Frequently Asked Questions
What is the difference between BMR and TDEE?
BMR is the calories you burn at complete rest. TDEE (total daily energy expenditure) is BMR multiplied by an activity factor to include movement and exercise. BMR is the baseline; TDEE is the fuller picture of what you burn in a typical day.
Why does the Mifflin-St Jeor equation matter?
It is the equation this calculator uses because studies have shown it predicts resting metabolic rate more accurately for the general population than older formulas. It bases the estimate on sex, age, weight, and height.
Should I eat at my BMR to lose weight?
Generally no. Eating below your BMR for long periods is not advised, because it is the energy your body needs at rest. Weight loss is usually pursued by eating below your TDEE — your activity-adjusted needs — not below your BMR.
Does BMR change over time?
Yes. BMR tends to decline with age and changes with weight and body composition — more muscle raises it, and significant weight loss lowers it. Recalculate periodically as your stats change to keep your calorie targets accurate.
