TDEE Calculator

How it works

The calculator runs the Mifflin-St Jeor equation, which derives your Basal Metabolic Rate from height, weight, age, and sex. For men the formula is 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5; for women it's the same except the constant is −161 instead of +5. That BMR number represents calories your body would burn lying completely still for 24 hours, covering organ function, cell repair, and temperature regulation. From there, the calculator multiplies your BMR by an activity factor ranging from 1.2 for desk-bound days with no exercise up to 1.725 for very hard training most days of the week, giving you a TDEE that reflects real life rather than a hospital bed scenario. Mifflin-St Jeor consistently outperforms the older Harris-Benedict equation in validation studies on modern populations, which is why most dietitians and research applications default to it.

When to use it

This calculator is most useful any time you're trying to make a deliberate change to body composition, whether that means trimming fat, adding muscle, or simply stopping unintentional weight drift. It gives you a starting calorie target grounded in your actual stats rather than a generic 2,000-calorie placeholder. Competitive athletes tracking performance nutrition, people returning from injury who've lost muscle mass, and anyone whose weight has stalled on a current plan will find a fresh TDEE estimate a useful reality check before adjusting intake.

Worked example

Take a 34-year-old woman who weighs 160 lbs (about 72.6 kg) and stands 5 ft 6 in (167.6 cm). Her BMR works out to roughly 1,516 calories per day. She works a desk job but lifts weights three days a week, so she selects the 'moderate exercise' activity multiplier of 1.55, landing her TDEE at approximately 2,350 calories. If her goal is slow, steady fat loss while preserving the muscle she's built, she'd look at eating somewhere in the 1,800-to-1,900-calorie range, since a 500-calorie daily deficit maps to roughly a pound of fat loss per week on average, and a smaller deficit still moves the needle while keeping training quality high.

Tips for an accurate result

• Weigh yourself in the morning after using the bathroom and before eating for the most consistent input number. A single weigh-in can be off by 2 to 5 lbs depending on hydration, so using a 7-day average gives the calculator a cleaner starting point.
• Honest activity selection is where most people go wrong. The 'moderately active' multiplier assumes genuine moderate-intensity effort on those exercise days, not a casual 20-minute walk. If your workouts are hard and consistent, use the higher multiplier; if they're scattered and short, stay conservative.
• TDEE estimates carry an inherent margin of error of roughly 10 to 15 percent because individual metabolic variation is real. Treat the output as a starting hypothesis, track your actual weight trend for two to three weeks, and adjust by 100 to 200 calories in either direction based on results.
• Body composition changes over time, and so does your TDEE. Losing 15 to 20 lbs lowers your BMR meaningfully because a lighter body costs less to run. Recalculate every 10 to 15 lbs of weight change rather than assuming your original number still holds.
• If you wear a fitness tracker, compare its daily calorie estimate against your TDEE result as a sanity check. The two won't match perfectly, but if they're more than 300 to 400 calories apart consistently, one of your inputs is probably off.