Calorie calculator

The three numbers, and which one you actually eat

People look for a calorie calculator, a TDEE calculator and a BMR calculator as though they were three different tools. They are three steps of one sum, and only the last one is a number you eat.

BMR, your resting rate

What your body would burn over a day spent lying completely still: heart, lungs, brain, temperature, the work of being alive. It is calculated here with the Mifflin St Jeor equation, the most accurate of the common formulas for people who are neither extremely lean nor extremely heavy. It is the floor. Eating at it is not a plan, it is a warning sign.

TDEE, what you actually burn

BMR multiplied by an activity factor between 1.2 and 1.9, covering walking, standing, training, and the energy spent digesting. This is your maintenance: eat it and, roughly speaking, your weight holds. It is the honest answer to "how many calories should I eat" for anyone not trying to change.

Your target

TDEE adjusted for the goal. Losing takes about 20 percent off, which for most people is 300 to 600 calories and around half a kilo a week. Building adds about 10 percent, because a bigger surplus mostly buys fat. The macro calculator takes this same number and splits it into protein, carbs and fat.

Where this goes wrong, honestly

Two places, and neither is the equation.

• The activity multiplier. This is the softest input in the whole calculation and almost everyone picks one too high. A desk job with three gym sessions is lightly active, not very active. If the scale has not moved in three weeks, lower this before you cut calories again.
• The target going stale. A lighter body costs less to run. Maintenance falls as you lose, so January's deficit is April's maintenance. Come back every four to six kilos. There is more on this in the guide to finding your number.

And the 7,700 calories per kilo figure behind the weekly estimate is an average of tissue that is part fat and part lean. It is a working number, not a law, which is why the panel says "if you hold it" rather than promising anything.

Sources

• A new predictive equation for resting energy expenditure in healthy individuals (Mifflin St Jeor), American Journal of Clinical Nutrition, 1990
• Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults, Journal of the American Dietetic Association, 2005
• Human energy requirements: report of a joint FAO, WHO and UNU expert consultation, Food and Agriculture Organization, 2004
• Quantification of the effect of energy imbalance on bodyweight, The Lancet, 2011

How this was made

Written by Abdullah Javaid, founder of Calfit, drafted with AI assistance and edited by hand. BMR comes from the Mifflin St Jeor equation, and maintenance multiplies it by an activity factor from 1.2 to 1.9. The target is about 20% under maintenance to lose fat or 10% over to build, and the weekly estimate divides the daily gap by 7,700 kcal per kilogram.

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