Calorie Calculator
Maintenance calories from the Mifflin-St Jeor equation and an activity factor, with sex-aware floors applied to the weight-loss target.
Calorie Calculator workspace
Parameters Configuration
Ready for calculations
Configure parameters on the left and press Calculate.
Using Calorie Calculator
Set your age on the slider. The equation is not valid below 10 and the field will not accept it.
Choose male or female — the Mifflin-St Jeor constant differs by sex.
Enter weight in kilograms and height in centimetres.
Pick the activity band that matches your actual week, from sedentary at 1.2 through to extra active at 1.9.
Read the maintenance figure, the resting rate beneath it, and the loss and gain targets.
Mifflin-St Jeor gives the resting rate, which is then multiplied by an activity factor between 1.2 and 1.9 to reach total daily energy expenditure. The weight-loss target takes 500 kcal off that total and stops at a floor of 1,500 kcal for men and 1,200 kcal for women, saying so when the floor is what is being displayed.
This calculator estimates how much energy you burn in a day, then subtracts or adds 500 kcal to give loss and gain targets. It is a prediction from four inputs, not a measurement, and the honest way to use it is as an opening bid that you revise against the scale.
Mifflin-St Jeor, multiplied by an activity band
Resting energy expenditure comes from the Mifflin-St Jeor equation, published by Mifflin, St Jeor and colleagues in the *American Journal of Clinical Nutrition* in 1990:
Men: BMR = 10 x weight(kg) + 6.25 x height(cm) - 5 x age + 5
Women: BMR = 10 x weight(kg) + 6.25 x height(cm) - 5 x age - 161That resting figure is then multiplied by the activity factor you select: 1.2 for sedentary, 1.375 lightly active, 1.55 moderately active, 1.725 very active, 1.9 for a physical job plus training. The product is your total daily energy expenditure.
Take a 32-year-old woman of 68 kg and 163 cm who selects lightly active. Resting rate is 680 + 1018.75 - 160 - 161 = 1,378 kcal. Multiplied by 1.375 that gives 1,894 kcal a day to hold her weight, and a loss target of 1,394 kcal.
The two places the estimate goes wrong
Predictive equations sit within roughly 10% of measured resting expenditure for most adults, which on a 2,000 kcal maintenance figure is a 200 kcal band before you have eaten anything. Only indirect calorimetry measures the real number.
The larger error is the activity factor, because you choose it yourself. The gap between 1.375 and 1.55 is more than 240 kcal for the woman above, and almost everyone rates their own week generously. If your weight has been stable, your actual maintenance intake is a better figure than anything this page produces. Weigh yourself over a fortnight, hold intake steady, and adjust from what the trend does rather than from the prediction.
Why the deficit target sometimes refuses to go lower
The arithmetic linking a 500 kcal daily deficit to about 0.45 kg of fat a week comes from the rough 7,700 kcal energy content of a kilogram of body fat. Real loss runs slower than that line predicts, because resting expenditure falls as body mass falls and because adherence is imperfect.
For a small or older person the subtraction can produce a number nobody should eat to. A sedentary 60-year-old woman of 55 kg and 158 cm has a maintenance figure near 1,292 kcal; taking 500 off leaves 792. The tool therefore applies a floor — 1,500 kcal for men and 1,200 for women — and tells you when the floor is what you are looking at rather than silently displaying it as a target. If the floor binds, the answer is usually more activity rather than less food, and a dietitian rather than a calculator.
Who this is not for
The equation is not valid for children under 10, and the form will not accept an age below that. It is not valid in pregnancy or while breastfeeding, when energy needs rise on a schedule this model knows nothing about. It also has no view on where the calories come from; if you want to turn a target into grams of protein, carbohydrate and fat, the macro calculator does that conversion, and the protein intake calculator sets protein from body weight and training goal instead.
Everything runs locally in your browser and no figure you type is sent anywhere. Your inputs may be retained by your own browser so the form survives a reload. This page has not been reviewed by a clinician, and a calorie target is not medical advice — if you are managing diabetes, an eating disorder or any condition where intake is part of treatment, that target should come from the person treating you.
Frequently asked
How much can I trust the number this produces?
Predictive equations land within roughly 10% of measured resting expenditure for most adults, which is already a 200 kcal band on a 2,000 kcal maintenance figure. The bigger error is the activity factor, because you pick it yourself and most people pick generously. If your weight has been stable, what you currently eat is better evidence than any prediction.
Why does the weight-loss figure stop at 1,200 or 1,500 kcal?
Subtracting a flat 500 kcal from a small person's maintenance can produce a figure nobody should eat to. A sedentary woman of 55 kg and 158 cm maintains near 1,292 kcal, and 500 off that leaves 792. The tool holds the target at 1,200 kcal for women and 1,500 for men and tells you the floor is what you are looking at.
Why is my weight not moving on the target it gave me?
Usually because the activity band is too high, because intake is being under-recorded, or because resting expenditure has fallen as body mass has. Hold intake steady for a fortnight, track weight across the whole period rather than day to day, and adjust from the trend rather than recalculating.
Does this apply during pregnancy or breastfeeding?
No. Energy requirements in pregnancy and lactation rise on a schedule this equation knows nothing about, and deliberately eating at a deficit during either is not something to plan from a web page. Those figures should come from your midwife, obstetrician or dietitian.