Health
BMR Calculator
Find your Basal Metabolic Rate — the calories you burn at complete rest — from your sex, age, weight, and height. Compare the Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle equations side by side, updating as you type.
The modern default — the most accurate predictive equation for the general population.
Your details
Mix units freely — kg with feet is fine.
Sex
years
Basal metabolic rate · Mifflin-St Jeor
1,370kcal/day
All three estimates
Mifflin-St Jeor
1,370
Harris-Benedict
1,430
Katch-McArdle
—
Katch-McArdle needs a body-fat %. Pick it above to fill the third cell.
With activity (TDEE)
Sedentary1,644kcal
Lightly active1,884kcal
Moderately active2,124kcal
Very active2,364kcal
Extra active2,603kcal
Try an example
No sign-up · Free
The basics
What your BMR tells you
Basal Metabolic Rate is the energy your body spends doing nothing — keeping your heart beating, your lungs working, your cells repairing. It's the floor of your daily calorie burn, and the foundation every diet or calorie target is built on top of.
rest, not activity
The cost of just existing
BMR is what you'd burn lying still, awake and fasted, for a full day. It's by far the biggest slice of how many calories you use — bigger than exercise for almost everyone.
≈ 60–70% of daily calories
BMR ≠ RMR ≠ TDEE
Three terms, easy to confuse
BMR is the strict at-rest measure; RMR is the same idea measured loosely and reads a little higher; TDEE is BMR scaled up for everything you actually do in a day.
TDEE = BMR × activity
Method
Work out BMR by hand
The Mifflin-St Jeor equation in three steps. Once your numbers are in metric, it's just arithmetic.
- 1
Get to metric
The equation works in kilograms and centimetres. Convert pounds to kg (÷ 2.205) and feet-inches to cm (× 2.54 per inch).
145 lb → 65.8 kg · 5 ft 5 in → 165 cm - 2
Build the common term
Multiply weight by 10, height by 6.25, and age by 5, then combine: 10×kg + 6.25×cm − 5×age. This part is identical for men and women.
10×65 + 6.25×165 − 5×30 = 1,531 - 3
Apply the sex constant
Add 5 for men, or subtract 161 for women. That single constant is the only thing that differs between the two.
1,531 − 161 = 1,370 kcal/day (woman)
Reference
The three BMR equations
Every BMR figure comes from one of these published formulas. Here's each equation and when to reach for it.
men: 10·kg + 6.25·cm − 5·age + 5 · women: − 161
Mifflin-St Jeor (1990)
The most accurate predictive equation for the general population and the modern standard. Use it unless you have a specific reason not to.
The engine default for everyone here
men: 88.362 + 13.397·kg + 4.799·cm − 5.677·age
Revised Harris-Benedict (1984)
The original 1919 equation, revised in 1984. Still widely cited, but it tends to overestimate BMR by a small margin versus Mifflin-St Jeor.
women: 447.593 + 9.247·kg + 3.098·cm − 4.330·age
370 + 21.6 · lean body mass(kg)
Katch-McArdle
Ignores height, age, and sex and reads only lean mass — so it needs a body-fat measurement. The best choice for lean or athletic people; without a body-fat number it can't run.
LBM = weight × (1 − body fat % / 100)
Worked examples
One body, three equations
Pick a person and watch all three formulas compute their BMR from the same numbers — the quickest way to see how far the equations disagree.
Given 65 kg, 165 cm, 30 years, 25% body fat
Mifflin-St Jeor
10×65 + 6.25×165 − 5×30 = 1531
1531 − 161 = 1,370 kcal/day
≈ 1,370 kcal/day
Harris-Benedict
447.593 + 9.247×65 + 3.098×165 − 4.330×30
= 1,430 kcal/day
≈ 1,430 kcal/day
Katch-McArdle
65 × (1 − 25/100) = 48.8 kg
370 + 21.6 × 48.8 = 1,423 kcal/day
≈ 1,423 kcal/day
Same body, three answers. Mifflin and Harris-Benedict use weight, height, and age; Katch-McArdle ignores them and reads only lean mass — which is why it diverges most when body fat is unusually high or low.
Where it shows up
Why BMR matters
BMR is rarely the end goal — it's the input that makes everything else in nutrition planning possible.
the base of TDEE
Daily calorie targets
Scale BMR by your activity level to get your TDEE, then adjust for a goal. Every calorie target starts here.
deficit & surplus
Diet planning
Knowing your resting burn is how you set a safe deficit for fat loss or a surplus for muscle gain — without guessing.
splits & grams
Macros & protein
Once you have a calorie target, a macro split and your protein goal follow from it.
Worth knowing
Things the number won't tell you
BMR is a useful estimate, not a fact about your metabolism. A few things worth keeping in mind.
BMR ≠ what you should eat
It's a floor, not a meal plan
Eating only your BMR while living an active life creates a steep deficit. The number to build a diet around is your TDEE — BMR scaled for activity.
eat your TDEE, not your BMR
predicted, not measured
±10% is normal
These equations predict an average. Your real metabolism can sit comfortably above or below the estimate; only indirect calorimetry measures it directly.
lab vs equation can differ by 100+ kcal
age, muscle, sex
It shifts over a lifetime
BMR drifts down with age as muscle is lost, falls when you lose weight, and runs lower on average in women than men of the same size.
≈ −2% per decade after 20
equations disagree
The formula matters
Different formulas give different answers for the same body. Compare them in the tool above and treat the spread, not any one number, as your range.
Mifflin vs Harris ≈ 100 kcal apart
Quick chart
BMR by weight and age
A fast lookup: find your weight down the side and your age across the top to read an approximate BMR, at an average height for each sex.
BMR in kcal/day at 165 cm height (Mifflin-St Jeor).
| Weight | 20 yr | 30 yr | 40 yr | 50 yr | 60 yr |
|---|---|---|---|---|---|
| 50 kg(110 lb) | 1,270 | 1,220 | 1,170 | 1,120 | 1,070 |
| 60 kg(132 lb) | 1,370 | 1,320 | 1,270 | 1,220 | 1,170 |
| 70 kg(154 lb) | 1,470 | 1,420 | 1,370 | 1,320 | 1,270 |
| 80 kg(176 lb) | 1,570 | 1,520 | 1,470 | 1,420 | 1,370 |
| 90 kg(198 lb) | 1,670 | 1,620 | 1,570 | 1,520 | 1,470 |
| 100 kg(220 lb) | 1,770 | 1,720 | 1,670 | 1,620 | 1,570 |
Read your weight on the left and your age across the top. Shorter or taller than 165 cm? Each 1 cm of height adds about 6 kcal/day — run the tool above for your exact figure.
FAQ
Common questions
BMR — Basal Metabolic Rate — is the number of calories your body burns at complete rest just to stay alive: breathing, circulating blood, regulating temperature, repairing cells. It's measured lying still, awake, and fasted, and it's the single largest part of your daily calorie burn, usually 60–70%.
Most calculators use the Mifflin-St Jeor equation: for men, BMR = 10×weight(kg) + 6.25×height(cm) − 5×age + 5; for women the last term is −161 instead of +5. So a 65 kg, 165 cm, 30-year-old woman has a BMR of 10×65 + 6.25×165 − 5×30 − 161 = 1,370 kcal/day.
For the general population, Mifflin-St Jeor (1990) is the most accurate predictive equation and is the modern default. Katch-McArdle can be more accurate for lean, athletic people because it's based on lean body mass — but only if you have a reliable body-fat measurement. Harris-Benedict, the classic, tends to run slightly high.
BMR is calories at complete rest under strict conditions. RMR (Resting Metabolic Rate) measures roughly the same thing under looser conditions and reads a touch higher — the two are often used interchangeably. TDEE (Total Daily Energy Expenditure) is BMR multiplied by an activity factor: it's your full daily burn including movement, exercise, and digesting food.
No. BMR is what you'd burn lying in bed all day — eating only that much, while moving and exercising, would create a large deficit. To find a sensible calorie target, scale BMR up to your TDEE by your activity level, then adjust from there for a weight goal.
Because they use different equations. Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle can disagree by 100–200 kcal for the same person — Harris-Benedict runs high, Katch-McArdle depends entirely on the body-fat number you enter. The estimates are predictions, not measurements, so treat any single figure as a ballpark.
BMR falls with age (you lose metabolically active muscle over time), with weight loss (a smaller body costs less to run), and with losing muscle. It's also lower, on average, in women than in men of the same size, mostly because of differences in muscle and fat distribution.
Yes — muscle is more metabolically active at rest than fat, so more lean mass means a higher BMR. The effect is real but modest: roughly 10–13 kcal per kg of muscle per day. That's exactly why Katch-McArdle, which is built on lean mass, can be the better equation for very muscular or very lean people.
Keep going
Related calculators
Keep reading
Further reading
Health
How to Calculate BMI (Body Mass Index), With the Formula and Examples
BMI = weight in kilograms ÷ height in metres squared. If you measure in pounds and inches, BMI = 703 × weight (lb) ÷ height (in) squared. This guide shows both formulas worked end to end, the standard WHO category table, and what BMI can and cannot tell you.
Ugo Charles
Math
How to Calculate GPA (Grade Point Average), Step by Step
To calculate GPA, convert each letter grade to its point value on the 4.0 scale, multiply each by the course's credit hours to get quality points, sum those quality points, and divide by the total credit hours. This guide walks through the formula, a full worked example, weighted versus unweighted GPA, and cumulative GPA across semesters.
Ugo Charles
Finance
How CD Interest Is Calculated: APY, Compounding, and Penalties
CD interest follows A = P(1 + r/n)^(nt). Why banks quote APY and not the rate, how compounding frequency moves the total, and what breaking early costs.
Ugo Charles
Written by
UC
Author
Ugo CharlesBuilt and fact-checked against our editorial standards · Last updated June 2026
Did this solve your problem?