Your TDEE is the total calories you burn in a day — your resting metabolism plus everything you do on top of it. Eat around that number and your weight holds; eat 500 fewer calories a day and you lose about a pound a week, 1,000 fewer and about two. This calculator estimates all three from your body stats and how active you are.
"How much should I eat?" almost always comes down to one number you can't see: total daily energy expenditure. It's the sum of your resting metabolism and every calorie you spend moving. Get a good estimate of it and the rest — losing, maintaining, or gaining — is just arithmetic around that baseline.
BMR, TDEE, and the number you actually use
Your basal metabolic rate is what you'd burn lying in bed all day: the energy for your heart, lungs, brain, and cells. It's the biggest slice of the pie, usually 60–70% of the total. Your TDEE takes that resting figure and multiplies it by an activity factor to fold in walking, working, fidgeting, and exercise. TDEE is the number to plan meals around, because it reflects a real day, not a resting one.
Turning your TDEE into a goal
A pound of body fat stores roughly 3,500 calories, so a 500-calorie daily deficit adds up to about a pound a week and 1,000 a day to about two. That's the math behind the toggle on the result card. It's a useful approximation, not a physical law — metabolism adapts as you lose, so expect to recalibrate every few weeks rather than assume the first number holds forever.
How accurate is it — and where it isn't
The default here is the Mifflin-St Jeor equation, the one most dietitians reach for; it lands within about 10% of measured resting expenditure for most adults. If you enter a reliable body-fat percentage, the calculator switches to Katch-McArdle, which estimates your burn from lean mass and tends to fit better at the extremes — very lean or very muscular. Neither can see your genetics, medications, thyroid, or how much you unconsciously move, so treat the output as a smart starting point you refine against the scale.
Numbers are a tool, not a green light. Talk to a clinician before making big changes if any of these apply:
- You're pregnant or breastfeeding
- You have diabetes, heart, kidney, or thyroid conditions
- You have a history of an eating disorder
- Your target lands below roughly 1,200 calories a day (women) or 1,500 (men)
Eating too little slows your metabolism and rarely lasts. A sustainable, supported plan beats an aggressive one you can't hold.
How this calculator works
It estimates your BMR, multiplies by your activity factor to get TDEE, then subtracts the deficit for your selected goal. Without a body-fat entry it uses Mifflin-St Jeor: for men, 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5; for women, the same with − 161 at the end. With a body-fat entry it uses Katch-McArdle: 370 + 21.6 × lean body mass(kg). Activity multipliers run from 1.2 (sedentary) to 1.9 (extra active), and a loss goal applies a 500- or 1,000-calorie daily deficit — capped at a safe minimum so it never suggests eating too little. The CDC considers 1–2 pounds a week a sustainable pace. Everything runs in your browser; nothing you enter is transmitted or stored.
Common questions
Your BMR (basal metabolic rate) is what your body burns at complete rest just to keep you alive — breathing, circulation, temperature. Your TDEE (total daily energy expenditure) is that BMR multiplied by an activity factor to account for everything you do on top of resting: walking, working, and exercise. TDEE is the number that matters when you're planning what to eat.
It's a well-validated starting point, not a lab measurement. Predictive equations like Mifflin-St Jeor land within about 10% of measured energy expenditure for most people, but genetics, muscle mass, and how much you move day to day all shift the real number. Use the estimate for a week or two, watch how your weight actually responds, and adjust from there.
Be honest — most people overestimate. "Sedentary" fits a desk job with little exercise; "lightly active" is exercise one to three days a week; "moderately active" is three to five days; "very active" is hard training six or seven days a week or a physically demanding job. If you're between two, pick the lower one and let your results guide you.
Only if you have a reliable measurement. When you do, the calculator switches to the Katch-McArdle equation, which bases your BMR on lean body mass and is often more accurate — especially if you're very lean or carry a lot of muscle. Leave it blank and it uses Mifflin-St Jeor, which needs only your height, weight, age, and sex.
For many people, yes — the CDC considers 1 to 2 pounds a week a safe, sustainable pace. But a 1,000-calorie daily deficit is a lot if you're smaller to begin with, and eating too little backfires. This tool won't take your target below a safe floor, and if weight loss is a real goal, a clinician can help you do it in a way that lasts.