Free BMR Calculator
What is BMR?
Basal Metabolic Rate (BMR) is the energy your body needs to stay alive at rest — powering your heart, lungs, brain, and cell repair. It's the largest single part of your daily calorie burn, typically 60–70%. Everything you do on top of that (moving, exercising, digesting) is added later to get your total daily need.
The four equations, side by side
All three age-and-size formulas below are run on the same two reference bodies, so the differences you see are the equations themselves rather than different inputs. Reference man: 35-year-old man, 5'10" (178 cm), 82 kg. Reference woman: 35-year-old woman, 5'5" (164 cm), 68 kg.
| Equation | Man | Woman | Notes |
|---|---|---|---|
| Mifflin–St Jeor (1990) | 1763 kcal | 1369 kcal | Default here — most accurate for the general adult population |
| Revised Harris–Benedict (1984) | 1842 kcal | 1433 kcal | Roza & Shizgal reworking of the original |
| Harris–Benedict (1918) | 1848 kcal | 1445 kcal | The original; tends to run high on modern populations |
The spread between the highest and lowest prediction is 85 kcal/day for the reference man. That is the honest margin of error on any predicted BMR: useful as a starting point, not a measurement. Katch–McArdle is not in the table because it needs a body-fat percentage rather than age and height — enter yours in the calculator above to see it.
BMR formulas explained
- Mifflin–St Jeor (1990): the modern default. Validated as the most accurate predictive equation for the general population.
Men: 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
Women: 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161 - Revised Harris–Benedict (1984): an updated version of the classic equation; very close to Mifflin for most people.
- Harris–Benedict (1919): the original equation, still widely referenced but tends to run slightly high.
- Katch–McArdle: based on lean body mass, so it needs your body-fat percentage. Often the most accurate for lean, muscular people.
BMR = 370 + 21.6 × lean body mass(kg)
Which formula should I use?
Start with Mifflin–St Jeor — it's the best general choice. If you know your body-fat percentage and are athletic, tryKatch–McArdle for a lean-mass-based estimate. The calculator shows every formula together so you can see the range.
What affects your BMR?
- Muscle mass — more lean tissue raises BMR.
- Body size — taller, heavier bodies burn more at rest.
- Age — BMR gradually declines with age.
- Sex — men usually have a higher BMR due to more muscle.
How BMR falls with age
Mifflin–St Jeor subtracts 5 kcal per year of age, so the drop is steady and predictable when body size stays the same. Holding the reference bodies fixed:
| Age | Man (82 kg, 178 cm) | Woman (68 kg, 164 cm) |
|---|---|---|
| 20 | 1838 kcal/day | 1444 kcal/day |
| 30 | 1788 kcal/day | 1394 kcal/day |
| 40 | 1738 kcal/day | 1344 kcal/day |
| 50 | 1688 kcal/day | 1294 kcal/day |
| 60 | 1638 kcal/day | 1244 kcal/day |
| 70 | 1588 kcal/day | 1194 kcal/day |
That is about 50 kcal/day per decade on paper. In practice most people lose muscle over the same period, so the real fall is steeper — which is the main argument for resistance training as you get older.
What your daily burn is actually made of
BMR is the biggest slice but not the only one. A typical day breaks down roughly like this:
- BMR — about 60–70%. Keeping you alive: brain, heart, kidneys, liver and cell turnover.
- Thermic effect of food — about 10%. The cost of digesting and processing what you eat. Protein is the most expensive to process (roughly 20–30% of its calories), carbohydrate is in the middle, fat is the cheapest.
- NEAT — 15% or more. Non-exercise activity: walking, fidgeting, standing, housework. This is the most variable component between two otherwise identical people.
- Exercise — 0–15% for most people. Usually smaller than people expect. An hour of moderate exercise rarely exceeds 400–600 kcal.
From BMR to daily calories
Your BMR alone isn't how much you should eat — you also burn calories moving around. Multiply BMR by an activity factor with theTDEE calculator, or jump straight to a goal-based target and macros with thecalorie calculator. This tool provides general information and is not medical advice.
Here is what that multiplication looks like for the two reference bodies, so you can see the size of the jump before you calculate your own:
| Activity level | ×BMR | Man | Woman |
|---|---|---|---|
| Sedentary Little or no exercise, desk job | 1.2 | 2115 kcal | 1643 kcal |
| Lightly active Light exercise 1–3 days/week | 1.375 | 2423 kcal | 1882 kcal |
| Moderately active Moderate exercise 3–5 days/week | 1.55 | 2732 kcal | 2122 kcal |
| Very active Hard exercise 6–7 days/week | 1.725 | 3040 kcal | 2362 kcal |
| Extra active Physical job or 2×/day training | 1.9 | 3349 kcal | 2601 kcal |
The gap between sedentary and extra active is 1234 kcal/day for the reference man — more than most people's entire deficit. Picking the right activity level matters more than picking the right BMR equation.
Once you have a target, the practical question is what to eat against it. Start with high-protein foods to cover the macro that protects lean mass, fill volume with low-calorie foods, and log the lot in the free calorie tracker.
More free calculators
BMR calculator FAQ
Is this BMR calculator free?
Yes — completely free, no sign-up, no ads. It runs entirely in your browser.
What is BMR?
BMR (Basal Metabolic Rate) is the number of calories your body burns at complete rest to keep essential functions running — breathing, circulation, and cell repair. It typically accounts for 60–70% of the calories you burn each day.
Which BMR formula is most accurate?
For most people the Mifflin–St Jeor equation is the most accurate and is the default here. If you know your body-fat percentage, the Katch–McArdle formula can be more precise because it is based on lean body mass.
What is the difference between BMR and TDEE?
BMR is your resting burn. TDEE adds activity and digestion on top. To get from BMR to the calories you can actually eat, use our TDEE calculator.
Why is my BMR different between formulas?
Each equation was derived from a different study population, so they weight height, weight, and age slightly differently. The calculator shows all of them side by side so you can compare.
What is a normal BMR?
Most adults land between roughly 1,200 and 1,900 kcal/day. For reference, Mifflin–St Jeor predicts about 1763 kcal/day for a 35-year-old man, 5'10" (178 cm), 82 kg, and about 1369 kcal/day for a 35-year-old woman, 5'5" (164 cm), 68 kg. Your own figure scales with your size, so a bigger body burns more at rest.
How much does BMR drop with age?
Holding height and weight constant, Mifflin–St Jeor subtracts 5 kcal for every year of age — so about 50 kcal/day per decade. From 20 to 70 that is a fall of 250 kcal/day for our reference man and 250 kcal/day for our reference woman. Real-world declines are usually larger because people also lose muscle.
Should I eat my BMR?
No. BMR is what you burn lying still all day, so eating exactly your BMR while living a normal life creates a large unintended deficit. Multiply it by an activity factor first with the TDEE calculator, then subtract from that number if you want to lose weight.
Can I raise my BMR?
Only modestly, and slowly. Adding lean mass through resistance training is the one lever with a real effect, but muscle burns roughly 13 kcal/kg/day at rest — a hard-won 5 kg of muscle is worth about 65 kcal/day. Eating enough and avoiding prolonged severe deficits matters more, since chronic under-eating lowers resting expenditure.
Is BMR the same as RMR?
Almost. BMR is measured under strict conditions — fasted, fully rested, in a thermoneutral room after overnight sleep. RMR (resting metabolic rate) uses relaxed conditions and comes out roughly 5–10% higher. Predictive equations like Mifflin–St Jeor are fitted to measured RMR, so in practice the terms are used interchangeably.