EstimatorBMR Calculator
Most BMR calculators quietly use one formula. This one runs all three major equations — Mifflin-St Jeor, Harris-Benedict and body-fat-based Katch-McArdle — so you can see the range, then turns each into TDEE by activity.
How it works
BMR is the energy your body burns at complete rest — breathing, circulation, cell repair. Mifflin-St Jeor (1990): 10×kg + 6.25×cm − 5×age + 5 (men) or − 161 (women). Harris-Benedict (revised 1984) uses different coefficients and tends to read slightly higher. Katch-McArdle skips sex and age entirely: 370 + 21.6 × lean body mass, so it wins when body composition is unusual — very muscular or very high body fat. Multiply any BMR by 1.2–1.9 for activity to get TDEE, your real daily burn.
Formula & worked example
Formula: Three published equations are shown side by side. Mifflin-St Jeor: 10 × kg + 6.25 × cm − 5 × age (+ 5 men, − 161 women). Harris-Benedict (revised): men 88.362 + 13.397 × kg + 4.799 × cm − 5.677 × age; women 447.593 + 9.247 × kg + 3.098 × cm − 4.330 × age. Katch-McArdle: 370 + 21.6 × lean body mass (kg). TDEE = BMR × activity factor.
Worked example: An 80 kg, 180 cm, 30-year-old man: Mifflin-St Jeor gives 1,780 kcal, Harris-Benedict 1,854 and Katch-McArdle at 15% body fat 1,839 — an average of 1,824. His sedentary TDEE from the Mifflin figure is 1,780 × 1.2 = 2,136 kcal.
When to use this
- You are setting a calorie target from scratch and want the resting-burn figure every target is built on.
- An app or diet plan handed you a number and you want to check it against the three standard equations.
- Your weight has changed by several kilos and a target that once worked has quietly stopped fitting.
- You lift seriously or carry a lot of body fat and suspect the one-formula calculators are missing your build.
How to use it, step by step
- Enter sex and age — both move the Mifflin-St Jeor and Harris-Benedict results.
- Pick metric or imperial and enter weight and height; imperial entries are converted automatically.
- Add a body fat percentage if you have one, so the Katch-McArdle line has something to run on.
- Choose a headline formula, then compare all three figures and their average in the results.
- Read down the TDEE table and match the activity row to your typical week, not your best week.
What the inputs mean
| Input | What it is | Typical values |
|---|---|---|
| Sex and age | Inputs to the Mifflin-St Jeor and Harris-Benedict equations | Age 10 to 100 on this tool |
| Weight and height | Body size, in kg and cm or converted from lb and ft/in | The bigger the body, the higher the BMR |
| Body fat % | Used only by Katch-McArdle, which runs on lean body mass | Roughly 10 to 35% for most adults |
| Headline formula | Which of the three equations drives the headline figure and the TDEE table | Mifflin-St Jeor is the usual default |
Another worked example
A 28-year-old woman, 65 kg and 168 cm, with 28% body fat: Mifflin-St Jeor gives 1,399 kcal a day, Harris-Benedict 1,448 and Katch-McArdle 1,381 — a span of 1,381 to 1,448, averaging 1,409. Built on the Mifflin figure, her TDEE runs from 1,679 kcal sedentary to 1,924 kcal with light exercise and 2,168 kcal at moderate activity, which is the range a sensible eating target has to sit inside. These are population-formula estimates, not a lab measurement.
Frequently asked questions
Which BMR formula should I trust?
For most adults, Mifflin-St Jeor — it performed best in validation studies and is the dietitian default. If you know your body-fat percentage accurately and your build is far from average, Katch-McArdle may be closer. Comparing all three, as this calculator does, shows you the realistic range.
What is a good BMR?
There is no single "good" number — BMR scales with size. Adult men commonly fall between 1,600 and 2,000 kcal/day and women between 1,300 and 1,600, but a tall, heavy person will naturally sit above those ranges. What matters is how it compares to your intake and activity.
What is the difference between BMR and TDEE?
BMR is rest-only burn. TDEE (total daily energy expenditure) is BMR multiplied by your activity factor — 1.2 for sedentary up to 1.9 for athletes — and is the number that actually maintains your weight.
How do I measure my body fat for Katch-McArdle?
Options range from DEXA scans and smart scales to skinfold calipers and the US Navy tape-measure method. Even a rough estimate helps: at 80 kg, the difference between 15% and 25% body fat changes the Katch-McArdle result by about 170 kcal.
🔥 From BMR to a full eating target
The Calorie Calculator adds goals and macro splits on top of your TDEE.
Why does Katch-McArdle ignore my age and sex?
Because it never asks for them. It runs entirely on lean body mass — 370 plus 21.6 times your lean kilos — so two people with the same lean mass get the same result whatever their age or sex. That is its strength for unusual builds and its weakness when the body fat percentage you feed it is a guess.
Does my BMR fall as I lose weight?
Yes, on every equation here. Mifflin-St Jeor adds 10 kcal for every kilo you carry, so losing 5 kg lowers the estimate by about 50 kcal a day before age or height enter it at all. It is a small, predictable drift, and it is why a target set at the start of a diet deserves a fresh run every few kilos.