How to use
- 1Enter sex, age, height and weight in US or metric units.
- 2Pick your activity level and a formula — Mifflin-St Jeor is the default.
- 3Read your BMR, total daily energy expenditure and the targets to lose, maintain or gain.
- 4Choose a goal and a macro split to see grams of protein, carbohydrates and fat.
BMR and TDEE
Basal metabolic rate (BMR) is the energy your body uses at complete rest. The default Mifflin-St Jeor equation (1990) is 10 × weight in kg + 6.25 × height in cm − 5 × age, plus 5 for men or minus 161 for women; reviews have found it the most reliable of the common equations for healthy adults. The revised Harris-Benedict equation (Roza and Shizgal, 1984) is offered as an alternative. Total daily energy expenditure (TDEE) multiplies BMR by an activity factor: 1.2 sedentary, 1.375 lightly active, 1.55 moderately active, 1.725 very active and 1.9 extra active. For a 35-year-old man who is 5 ft 10 in and 180 lb, that gives a BMR of about 1,760 kcal and a TDEE of about 2,720 kcal at moderate activity.
Targets for weight loss and gain
The weight-loss target subtracts 500 kcal from your TDEE — the classic starting point often quoted as roughly 1 lb (0.45 kg) per week, although real-world loss slows as the body adapts. The gain target adds 300 kcal for a gradual increase. If the weight-loss figure falls below 1,200 kcal a day for women or 1,500 kcal for men, the tool flags it, because eating less than that is generally advised only under medical supervision.
Macro split and limits
Choose a goal and one of four splits — balanced (30% protein / 40% carbs / 30% fat), low carb (40/20/40), high carb (25/55/20) or high protein (40/35/25). Grams are calculated with 4 kcal per gram for protein and carbohydrates and 9 kcal per gram for fat. The equations were developed for adults and don’t apply to children and teens or during pregnancy and breastfeeding. All figures are estimates for information only, not medical or nutritional advice — consult a doctor or registered dietitian before starting a diet.
Frequently asked questions
How many calories should I eat a day?
To maintain your weight, roughly your TDEE. Individual needs can differ from any equation by a few hundred calories, so adjust based on how your weight actually changes over several weeks.
What is the difference between BMR and TDEE?
BMR is what you burn at complete rest; TDEE adds daily movement, exercise and digestion. TDEE is the number to plan your intake around.
Which formula should I choose?
Mifflin-St Jeor is the default and generally preferred for adults. The revised Harris-Benedict equation usually gives a slightly higher estimate.
How many calories should I cut to lose 1 pound a week?
The traditional rule is about 500 kcal a day, based on roughly 3,500 kcal per pound of body fat. In practice the rate slows over time, so treat it as a rough guide.
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