BMR Calculator

What is BMR?

Basal metabolic rate is an estimate of the energy your body would use over 24 hours while completely at rest.

Even lying still, your body is spending calories continuously: maintaining your heartbeat and circulation, breathing, running your brain, holding your body temperature steady, repairing cells and keeping your organs working.

BMR is the foundation of your total daily energy expenditure — typically the largest single share of it — but it excludes almost everything you actually do during a day.

BMR versus TDEE

These are related but distinctly different, and confusing them is the most consequential mistake on this topic.

BMR

The energy used at complete rest. It does not include walking, working, housework, exercise, or digestion.

TDEE

Total daily energy expenditure — your BMR plus everyday movement, planned exercise, non-exercise activity and the energy needed to digest food. A rough estimate comes from multiplying BMR by an activity factor:

These are broad bands. Two people picking the same level can genuinely differ by several hundred calories a day, mostly through how much they move outside training. Use the TDEE calculator to calculate your total daily energy expenditure properly.

BMR, maintenance calories and your target

The progression runs BMR → TDEE → calorie target, and each step is a different question.

Your BMR is what you burn at rest. Your TDEE is what you burn in total. Your calorie target is what you choose to eat, depending on whether you want to maintain, lose weight gradually, gain weight, support training or build muscle.

Someone with a BMR of 1,700 might have a TDEE of 2,300 once normal activity is counted. Eating 1,700 would not be maintenance for them — it would be a 600-calorie daily deficit, which is a very different plan from the one they thought they were following.

Once you have a total, the calorie calculator will estimate your daily calorie target, and the calorie deficit calculator works out a sustainable rate if you are eating to lose.

Should you eat the same calories as your BMR?

No, and this is worth being direct about because it is a common and consequential error.

BMR describes energy use under highly controlled resting conditions, not the energy needed to get through an ordinary day. Eating at your BMR while living normally means eating well below what you use.

A sensible daily target accounts for your total activity, your goals, your current weight, how fast you intend to change it, whether the target leaves room for enough protein, fibre, vitamins and minerals, any relevant health conditions, and professional advice where that applies.

How BMR is calculated

This calculator uses the Mifflin-St Jeor equation, developed from measurements on 498 adults and still the most reliable of the common predictive equations for resting energy in healthy people.

Men: BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age) + 5

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

A worked example

A 35-year-old man weighing 80kg at 180cm tall:

(10 × 80) + (6.25 × 180) − (5 × 35) + 5

800 + 1,125 − 175 + 5 = 1,755 kcal/day

That does not mean he should eat 1,755 calories. His real daily requirement includes movement, exercise and digestion on top.

What affects your BMR?

Body size

Larger bodies cost more to maintain, which is why height and weight both appear in the equation.

Muscle mass

Muscle is more metabolically active than fat, so two people of identical weight can have different resting needs. The equation does not measure body composition, so it cannot see this — one of its main limitations.

Age

Requirements generally fall with age, largely through changes in body composition and muscle mass. Age appears directly in the calculation.

Sex

The equation uses different constants for men and women because the groups it was derived from showed different average resting requirements.

Genetics, health and hormones

Normal physiological variation, illness, fever, thyroid conditions, pregnancy and some medications all affect energy expenditure. A general calculator cannot account for any of them.

How accurate is a BMR calculator?

It is an estimate from population data, not a measurement of you.

It is likely to be less representative if you have unusually high or low muscle mass, a very high or low body-fat percentage, a medical condition affecting metabolism, or have recently lost a substantial amount of weight.

The accurate way to measure resting energy expenditure is indirect calorimetry in a clinical or laboratory setting. For everyday meal planning, an equation-based figure is a perfectly reasonable starting point — provided it is treated as one.

BMR versus RMR

Basal metabolic rate is measured under tight conditions: fasted, fully rested, thermally neutral. Resting metabolic rate is measured under less restrictive conditions and comes out slightly higher.

In everyday calculators the terms are used interchangeably, because both describe resting energy expenditure and the difference is small relative to the error in any prediction equation. The Mifflin-St Jeor paper itself describes its equation as predicting resting energy expenditure.

Can you increase your BMR?

Not dramatically, and not through any single food, supplement or short routine. Be sceptical of anything marketed as a metabolism boost.

Resting needs do change as your body changes — through gaining or losing mass, building or losing muscle, ageing, pregnancy, illness, hormonal shifts, and sustained changes in intake.

Resistance training helps build and preserve muscle, which supports resting expenditure. The effect is real but gradual, measured in months rather than weeks, and modest next to the difference daily movement makes.

Does losing weight reduce your BMR?

Usually, yes. A smaller body needs less energy to maintain, and any muscle lost alongside fat reduces it further.

This is why a target set at the start of a weight-loss period stops working after a few months: the deficit you calculated has quietly shrunk as your maintenance fell. Recalculate after losing roughly 5–10% of your starting weight, after a significant change in activity or training, or after a marked change in body composition.

Is a higher BMR better?

No. BMR is not a score.

It largely reflects body size and composition, so a taller or heavier person will usually have a higher BMR than a smaller one without being any healthier. Treat it as an input for estimating energy needs, not a number to maximise.

Using your BMR to plan your nutrition

The BMR figure on its own does not tell you what to do. It becomes useful at the next step.

Estimate your total daily needs with the TDEE calculator, choose a target with the calorie calculator or calorie deficit calculator, then turn your calories into macro goals and set a protein figure with the protein calculator.

From there Mealiv can create a personalised meal plan around those targets, track what you actually eat against them, and monitor fibre, vitamins and minerals alongside the calories.

Important information

This calculator gives a general estimate for healthy adults aged 18 and over and is not a medical assessment. It cannot account for medical conditions, medication, pregnancy or individual metabolic variation. Speak with a GP, registered dietitian or other qualified healthcare professional before making significant changes to your diet, particularly if you have a health condition or a history of disordered eating.