Calorie calculator

How many calories should you eat?

A calorie calculator estimates how many calories to eat in a day to hold your weight, and how far to shift that number to lose or gain. It starts from your resting metabolism, the energy your body spends just staying alive, then scales it up for how much you move. The result is a maintenance figure with lose and gain targets built around it.

The energy you burn is your TDEE; the number here is its mirror, the energy you take in. Eat at maintenance and your weight holds. Eat under it and your body covers the gap from stored fat. That balance drives every result on this page.

Choosing your formula

The resting-metabolism formula is the assumption every calorie estimate rests on, so this tool puts the choice in your hands. Three are worth knowing.

Per CalculateMyTDEE's comparison of the two main equations, a 2005 systematic review found Mifflin-St Jeor carried the smallest mean error, about 1 kcal out in non-obese subjects and 1.5% in obese ones, while Harris-Benedict overestimated resting burn by 5 to 15%. That's why Mifflin leads here.

Offering the choice used to be unusual. It isn't any more: Calculator.net now offers the same three and publishes all three equations. Of the ten calorie calculators checked for this page on 9 September 2026, those two are the only ones that let you pick at all, and the other eight lock you into a single equation, usually Mifflin without saying so.

The dropdown that costs more than the formula

Every calculator on this search asks for an activity level. Five of them list the multipliers. Not one shows what picking the wrong one does to your number.

Which is odd, because it dwarfs the thing they all argue about. On this page's defaults, a 30 year old woman at 170 cm and 70 kg:

The dropdown is worth 3.5 times the formula debate. And it's the input you're least equipped to answer, because it asks you to grade your own week. CalculateMyTDEE's guide to activity levels puts it plainly: most people overestimate by one to two levels, and gym sessions three times a week is Moderate rather than Very Active.

Two habits make the number trustworthy. Pick the level that matches your job first and your training second, since a desk job dominates most weeks. Then check the estimate against reality: track intake and weight for two to three weeks, and if the weight isn't moving as the maintenance figure predicts, the multiplier is the input to correct, not the formula.

A worked example

The defaults: a 30 year old woman, 170 cm, 70 kg, exercising three to five days a week.

Her Mifflin-St Jeor resting burn is 1,452 calories, and the five activity levels take it from there:

Moderate is the default, so 2,251 is her maintenance. A 500 calorie deficit puts a loss target near 1,750.

Switch her to Harris-Benedict and the resting figure moves to 1,499, and maintenance to 2,323. Seventy-three calories, roughly a slice of bread. Move her one level on the dropdown instead and it's 254, roughly a meal component.

What a calorie deficit really does

A calorie deficit is eating fewer calories than your body spends, so it draws on stored fat to cover the gap. A pound of fat holds roughly 3,500 calories, which divided by seven gives the familiar rule: cut 500 a day for about a pound a week.

That rule holds for the first few weeks and decays after. Resting metabolism falls as the weight comes off, so a fixed 500 deficit returns less each month and the curve flattens. Month six never matches month one on the same intake. The calculator prints the standard targets as a starting point, and your own results across two to three weeks are the better guide.

Where the floors sit

Very low targets are where calorie arithmetic stops being harmless. The common guidance, which Healthline states on its own calculator page, is that dropping below about 1,200 calories a day for women or 1,500 for men makes adequate protein, vitamins and minerals hard to reach.

The fast-loss row can dip under those floors for smaller or older bodies. When it does, the arithmetic is still correct and the target has stopped being useful. Anyone eating that low for a medical reason needs a doctor or a registered dietitian involved.

Why men and women get different numbers

Sex shifts the result because it shifts body composition. Men on average carry more lean muscle, which burns more at rest, so Mifflin-St Jeor adds 5 to a man's resting figure and subtracts 161 from a woman's. That constant is the entire difference in the equation. A 70 kg man and a 70 kg woman of the same age and height land a couple of hundred calories apart before activity is counted, which is why one household calorie target rarely fits two people.

What this calculator can't do

It can't see your metabolism. Every equation here is a population average fitted to a group, and individual resting burn varies around that average for reasons including genetics, medication, thyroid function and lean mass that no tape measure captures.

It also can't audit your activity answer, which is the largest error in the whole calculation and the one input only you can improve.

Results are estimates and aren't medical or dietary advice. For decisions about your weight, health or diet, talk to a doctor or a registered dietitian.

Frequently asked questions

How many calories should I eat a day? It depends on your size, age, sex and how much you move. On this page's defaults, a 30 year old woman at 170 cm and 70 kg exercising three to five days a week maintains at about 2,250 calories, with a pound-a-week loss target near 1,750. Your own figure comes from the calculator above.

Does the activity level matter more than the formula? Yes, by roughly 3.5 times. On the same defaults, switching between Mifflin-St Jeor and Harris-Benedict moves maintenance by 73 calories, while being one activity level out moves it by 254. Sedentary against very active spans 1,016 calories. It is the input most worth getting right and the one people most often overstate.

What is a calorie deficit? A calorie deficit is eating fewer calories than you burn, which draws on stored energy to cover the difference. About 500 calories a day works out near a pound of fat a week at first, and the rate slows as you get lighter because resting metabolism falls with the weight.

Is 1,200 calories a day too low? For most adults it sits at the floor. The common guidance, which Healthline states on its own calculator page, is that below about 1,200 for women or 1,500 for men it becomes hard to get enough protein, vitamins and minerals. Eating that low for a medical reason needs a doctor or registered dietitian supervising.

Which calorie formula is most accurate? Mifflin-St Jeor is the default here. Per CalculateMyTDEE, a 2005 systematic review found it carried the smallest mean error, roughly 1 kcal in non-obese subjects and 1.5% in obese ones, against Harris-Benedict overestimating by 5 to 15%. Katch-McArdle can beat both if you know your body fat percentage, since it works from lean mass.

Do I have to count calories to lose weight? No. Counting is one method among several, and portion control, higher protein and cutting liquid calories all work without a tracker. The number here is a starting target rather than something you have to log against daily.

Sources

Fetched 9 September 2026.

• CalculateMyTDEE, Mifflin-St Jeor against Harris-Benedict, for the 2005 review figures
• CalculateMyTDEE, activity level multipliers, for the overestimation research
• Calculator.net calorie calculator, which publishes all three equations
• Healthline, how many calories per day, for the 1,200 and 1,500 floors
• NASM calorie calculator, which publishes the Mifflin-St Jeor equation
• American Cancer Society calorie counter, reviewed by ASCO
• TDEEcal.net activity levels guide, for the cross-check on a comparable body