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 you loss and gain targets. It's a prediction from four inputs, so it can't measure anything. Treat the number as an opening bid and revise it against what the scale tells you.
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 - 161The tool multiplies that resting figure by the activity factor you pick: 1.2 for sedentary, 1.375 lightly active, 1.55 moderately active, 1.725 very active, and 1.9 for a physical job plus training. The result is your total daily energy expenditure.
Say a 32-year-old woman of 68 kg and 163 cm picks lightly active. Her resting rate is 680 + 1018.75 - 160 - 161 = 1,378 kcal. Multiplied by 1.375, that's 1,894 kcal a day to hold her weight, and a loss target of 1,394 kcal.
The two places the estimate goes wrong
For most adults, predictive equations land within roughly 10% of measured resting expenditure. On a 2,000 kcal maintenance figure that's a 200 kcal band before you've eaten anything. Only indirect calorimetry measures the real number.
The bigger error is the activity factor, because you choose it yourself. For the woman above, the gap between 1.375 and 1.55 is more than 240 kcal, and almost everyone rates their own week generously. If your weight has been stable, what you're actually eating to maintain it is a better figure than anything this page produces. Weigh yourself over a fortnight, keep intake steady, and adjust based on what the trend does, not what the prediction said.
Why the deficit target sometimes refuses to go lower
The idea that a 500 kcal daily deficit loses 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, partly because resting expenditure falls as body mass falls and partly because nobody sticks to a plan perfectly.
For a small or older person, subtracting 500 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, and taking 500 off leaves 792. So the tool applies a floor (1,500 kcal for men and 1,200 for women) and tells you when you're looking at the floor, instead of silently showing it as your target. If the floor kicks in, the answer is usually more activity, not less food, and a conversation with a dietitian.
Who this is not for
The equation isn't valid for children under 10, and the form won't accept an age below that. It isn't valid in pregnancy or while breastfeeding either, 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 nothing you type is sent anywhere. Your browser may keep your inputs so the form survives a reload. This page hasn't been reviewed by a clinician, and a calorie target is not medical advice. If you're 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.