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What does your body burn at rest?

BMR Calculator

Your basal metabolic rate is what you'd burn lying still in bed all day — the engine idling. It's the foundation every calorie target is built on, and it is not the number you should eat.

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After 14 days of tracking

A calculator gets you close; your real trend gets you exact. Compare your two-week result against this table:

What you observeWhat to change
You're eating at your BMR and feel exhaustedYou're almost certainly under-eating. Add the activity multiplier and eat relative to TDEE, not BMR — for most people that's 400–900 kcal more per day.
Your BMR looks low for your sizeBody composition the formula can't see. Use it as a starting point, then let two weeks of real tracking correct it rather than trusting the estimate.
Your weight is stable but intake is near BMRYour true maintenance is higher than the estimate suggests, or logging is under-counting. Trust the scale trend over the formula — the trend is measured, the formula is predicted.
BMR dropped after significant weight lossExpected — a smaller body costs less to run, and some adaptation is normal. Recalculate at your new weight rather than holding on to old targets.

A formula gives you a starting point. Your own data gives you the answer.

PocketChomp learns your real maintenance from what you actually eat and how your weight actually moves — so you stop guessing from an equation that's never seen your body.

What this calculator does

It runs the Mifflin-St Jeor equation, the formula most clinical and research settings reach for first because it holds up better than the older Harris-Benedict across modern populations:

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

That’s the whole thing. Four inputs, one number. Worth understanding exactly because it explains the limitation: the equation has no way of knowing whether you’re carrying significant muscle or very little, and lean mass is the single biggest driver of resting burn. Two people matching on all four inputs can have genuinely different real rates.

Why BMR is not your calorie target

This is the mistake worth avoiding. BMR is what you burn doing nothing. Your actual daily burn — total daily energy expenditure, or TDEE — adds everything else:

  • Movement and exercise. Anywhere from 15% to 30%+ of total burn.
  • The thermic effect of food. Digestion itself costs roughly 10% of what you eat.
  • Non-exercise activity. Fidgeting, standing, walking to the kitchen. Varies enormously between people — several hundred calories a day between a restless person and a still one.

Multiply BMR by an activity factor (1.2 sedentary through 1.9 for hard training plus a physical job) and you get TDEE. That is the number intake decisions are made against. Eating at BMR when your TDEE is 800 kcal higher isn’t a careful deficit — it’s a crash diet you didn’t intend, and it usually ends in a binge rather than a result.

The honest limitation

Every BMR calculator on the internet, this one included, is a population-average prediction dressed up as a personal number. Mifflin-St Jeor lands within about 10% for roughly four out of five people — which still means a 1,600 kcal estimate could reasonably be 1,440 or 1,760, and for one person in five it’s further out than that.

So treat the output as a hypothesis, not a measurement. The way to find your real number is to eat at a consistent, logged intake for two weeks and watch what your weight actually does. The scale is measuring reality; the formula is guessing at it.

Frequently asked questions

What is BMR?

Basal metabolic rate — the energy your body spends staying alive with zero activity: breathing, circulating blood, maintaining temperature, repairing tissue, running your brain. Measured properly it's taken after a full night's sleep, fasted, at rest. For most people it accounts for 60–70% of everything they burn in a day.

Should I eat my BMR?

No — and this is the most common and most harmful misreading of the number. BMR excludes every calorie you spend moving, digesting, working and training. Eating at BMR means eating well under what you actually burn, usually by 400–900 kcal. Use TDEE for intake decisions; BMR is only the input that gets you there.

What's the difference between BMR and RMR?

BMR is measured under strict laboratory conditions — fully fasted, fully rested, thermally neutral. RMR (resting metabolic rate) is measured under looser real-world conditions and typically lands about 10% higher. The two get used interchangeably online, including by most calculators. The difference is smaller than the error bar on any formula estimate, so it rarely changes a decision.

How accurate is the Mifflin-St Jeor equation?

It's the most accurate of the widely used formulas, predicting measured BMR within about 10% for roughly 80% of people — but it only knows your height, weight, age and sex. It cannot see your body composition, and muscle is far more metabolically active than fat. Two people with identical stats and very different builds get the same estimate and have genuinely different rates.

Why is my BMR lower than I expected?

Usually body composition or age. Lean mass drives resting burn, so a smaller or less muscular body burns less at rest, and BMR declines gradually with age as lean mass falls. A low number isn't a verdict on your metabolism — it's an estimate from four inputs, and the honest way to test it is two weeks of consistent logging against your weight trend.

Can I raise my BMR?

Somewhat, and slowly. Adding lean mass raises resting burn, though the effect is modest — roughly 10–15 kcal per day per kilogram of muscle, so months of training might move it by 50–100 kcal. What moves your total burn far more is activity: daily movement and training swing your TDEE by hundreds of calories, which is why activity level matters more than chasing your basal rate.

Next, turn your BMR into a daily target with the TDEE calculator →