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Calorie Calculator

Calculators · Added 14 August 2026

Your body uses energy at rest to run its basic functions, and more on top of that for everything you do. This calculator estimates both: basal metabolic rate from one of three published equations, then daily energy expenditure by applying an activity factor. The formula used is named on the page, because which equation produced a number is part of the number.

Units
Sex
yrs
kg
cm

Moderate exercise three to five days a week.

Published 1990 and the usual default. Validated against indirect calorimetry as the most accurate of the common equations for a general adult population.

How to use the calorie calculator

  1. 1Choose metric or imperial units, then enter your age, sex, weight and height.
  2. 2Pick the activity level that matches a typical week, not your best one. Most people overestimate this.
  3. 3Choose a formula. Mifflin-St Jeor is the usual default; Katch-McArdle is more accurate but needs a body fat percentage.
  4. 4Press Calculate to see your BMR and your estimated daily requirement.
  5. 5The table shows targets for losing, maintaining and gaining. Read the disclaimer under it before acting on any of them.

Examples

A moderately active adult

Input
Male, 30 years, 180 cm, 80 kg, moderately active, Mifflin-St Jeor
Result
BMR 1,780 kcal · daily requirement about 2,759 kcal

The BMR is what the body uses at complete rest. The activity factor of 1.55 accounts for everything else.

The same person, sedentary

Input
Identical figures with a sedentary activity level
Result
Daily requirement about 2,136 kcal — over 600 kcal lower

The activity multiplier moves the answer far more than most people expect, which is why an honest choice matters.

Comparing the formulas

Input
Female, 30 years, 165 cm, 60 kg — Mifflin-St Jeor against Harris-Benedict
Result
BMR 1,320 kcal against about 1,384 kcal

A 63 kcal spread on identical inputs. No equation is definitive, which is the honest reading of both numbers.

About the calorie calculator

What BMR and TDEE actually mean

Basal metabolic rate is the energy your body uses doing nothing at all — maintaining temperature, circulating blood, running the brain, repairing tissue. For most adults it accounts for the majority of daily energy use, which surprises people who assume exercise dominates.

Total daily energy expenditure is BMR plus everything else: the energy cost of digesting food, deliberate exercise, and the large and variable category of non-exercise activity — walking, fidgeting, standing, household work. That last component varies enormously between individuals with similar routines, and it is the main reason two people of identical size and stated activity level can have genuinely different requirements.

The activity multiplier is a blunt attempt to capture all of it in one number. It is the least precise part of the calculation and the part with the largest effect on the result, which is an uncomfortable combination and a good reason to treat the output as an estimate to be tested rather than a target to be trusted.

Using the number honestly

The most reliable way to use a figure like this is as a hypothesis. Eat at the estimated maintenance level for two or three weeks, track weight with a consistent method, and see what actually happens. If weight is stable, the estimate was close. If it drifts, adjust the intake by a couple of hundred calories and repeat. Your own data beats any equation, because it accounts for everything the equation cannot see.

There are also good reasons not to chase the number too hard. Calorie labels carry meaningful error, portion estimation at home is imprecise, and daily weight fluctuates with water, sodium and digestion by amounts that dwarf a day's deficit. Weekly averages are informative; individual days mostly are not.

Finally, a deliberate note about limits. This page estimates energy requirements and nothing else. It says nothing about the composition of a diet, about micronutrients, or about whether any particular goal is appropriate for you — and it is not a substitute for advice from a doctor or a registered dietitian who knows your history. If you are managing a health condition, pregnant, or taking medication that affects appetite or metabolism, that conversation should come before any number on this page.

Frequently asked questions

Which formula should I use?
Mifflin-St Jeor unless you have a reason otherwise. It was published in 1990 and has validated better against indirect calorimetry than the older Harris-Benedict for a general adult population. Katch-McArdle is more accurate still because it works from lean mass rather than total weight — but only if you have a reliable body fat measurement, which most people do not.
How accurate is this?
It is a population estimate, not a measurement. These are regression equations fitted to groups, so they predict a group mean and an individual can sit several hundred calories either side for reasons the inputs cannot capture — body composition, thyroid function, medication, genetics. Use the number as a starting point and adjust based on what actually happens over a few weeks.
Why does the activity level change the answer so much?
Because the multiplier is applied to the whole BMR. Moving from sedentary (1.2) to moderately active (1.55) is a 29% increase in the final figure. This is also the input people get wrong most often — the honest question is what a typical week looks like, including the ones where training did not happen.
Where do the weight-loss numbers come from?
The conventional 7,700 kcal per kilogram of body mass, which is a rule of thumb rather than a physical constant. Real weight change is not linear: it slows as body mass falls, because a smaller body needs less energy, and metabolic adaptation reduces expenditure further during a sustained deficit. Treat a 500 kcal deficit as roughly half a kilogram a week at the start, and expect it to slow.
Is this medical advice?
No. This calculator provides an estimate for general informational purposes and is not medical advice. It does not diagnose anything and does not prescribe anything. Speak to a doctor or a registered dietitian before making significant dietary changes, particularly if you are pregnant, managing a health condition, taking medication, or considering an aggressive deficit.

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