How this calculator works

Three numbers matter, and they stack in order.

1. BMR, what your body burns doing nothing

Your basal metabolic rate is the energy you would burn lying in bed all day: heartbeat, breathing, brain, temperature. It is roughly 60 to 70 percent of everything you burn. This calculator uses the Mifflin St Jeor equation, which has been the standard since 1990 and is more accurate for modern bodies than the older Harris Benedict formula:

• Men: (10 x kg) + (6.25 x cm) - (5 x age) + 5
• Women: (10 x kg) + (6.25 x cm) - (5 x age) - 161

If you enter a body fat percentage we switch to Katch McArdle instead, which works from lean body mass rather than total weight: 370 + (21.6 x lean kg). For a lean, heavily muscled person that is the better estimate, because muscle and fat do not burn the same.

2. TDEE, what you actually burn in a day

Total daily energy expenditure is your BMR multiplied by how much you move. This is where almost everyone gets it wrong, usually by picking a level too high.

Level	Multiplier	What it actually means
Sedentary	1.2	Desk job, no structured training
Lightly active	1.375	1 to 3 sessions a week
Moderately active	1.55	3 to 5 sessions a week
Very active	1.725	6 to 7 sessions a week
Athlete or physical job	1.9	Two a days, or you are on your feet all day

A desk worker who lifts four times a week is moderately active, not very active. The gym is an hour. The other twenty three count too.

3. Your target, TDEE adjusted for the goal

A pound of body fat is roughly 3,500 calories, so a 500 calorie daily deficit is about a pound a week. That is the arithmetic behind the goal selector:

• Lose weight. Subtract. We cap the suggestion at 1 percent of bodyweight per week, because past that you start paying in muscle rather than fat.
• Maintain. Eat your TDEE. Useful if you are chasing performance or body recomposition rather than a number on the scale.
• Gain weight. Add, but less than people expect. A 250 to 500 calorie surplus builds muscle about as fast as your body can, and anything beyond it is mostly fat.

Where the macros come from

Protein is set first, because it is the one that protects muscle while you are in a deficit and builds it when you are in a surplus: around 1 gram per pound of bodyweight when cutting, slightly less when maintaining. Fat is set at roughly a quarter of your calories, enough for hormone production. Carbohydrate fills the rest, because that is what fuels hard training.

How to actually use the number

Treat it as a starting line, not a law. The formula is an estimate built from population averages, and your body is not an average.

1. Eat the target for two full weeks. Weigh yourself the same way every morning.
2. Compare the average of week two against the average of week one, not day to day. Daily weight is mostly water, salt and what is still in your gut.
3. If the scale is not moving the way you want, change calories by 100 to 200 a day. Not 500.
4. Recalculate after every 10 to 15 pounds of change, because a lighter body burns less.

Consistency beats precision. Someone who hits 2,200 calories most days will beat someone who calculates 2,147 and quits in a fortnight.

Frequently asked questions

How do you calculate TDEE?

Calculate your BMR with the Mifflin St Jeor equation, then multiply it by an activity factor between 1.2 and 1.9. A 195 pound, 32 year old man at 5 foot 11 has a BMR of about 1,857, so training four times a week (x1.55) puts his TDEE near 2,878 calories.

Are TDEE calculators accurate?

They land within roughly 10 percent for most people, which is close enough to start. They are least accurate at the extremes: very lean, very heavy, very old, very muscular, or anyone with a thyroid condition. That is why we offer the Katch McArdle option, and why the real answer comes from two weeks of your own scale data rather than any calculator.

What is the difference between BMR and TDEE?

BMR is what you burn at complete rest. TDEE is BMR plus everything else: training, walking, digesting food, fidgeting. TDEE is always the larger number and it is the one you eat against.

How many calories should I eat to lose weight?

Roughly 500 below your TDEE for about a pound a week. Going harder than 1 percent of bodyweight per week tends to cost muscle, tank training quality and wreck adherence, which is why this calculator will not suggest it.

How many calories to build muscle without getting fat?

A surplus of 250 to 500 calories. Muscle is built at a biological speed limit of maybe half a pound a week for most trained lifters, so a bigger surplus does not build it faster, it just adds fat you will have to diet off later.

Should I eat back the calories I burn training?

No. Your activity multiplier already includes training. Adding your watch's calorie estimate on top double counts it, and wearables routinely overestimate burn by 20 to 90 percent.

How often should I recalculate?

Every 10 to 15 pounds of bodyweight change, or any time your training volume shifts meaningfully. A body 20 pounds lighter needs noticeably fewer calories to run.

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This calculator is an educational estimate and is not medical advice. If you are pregnant, managing a medical condition, or have a history of disordered eating, speak to a doctor or registered dietitian before changing your intake.