Health & Fitness Calculators
A free TDEE calculator with BMR and daily calorie targets for cutting, maintaining and bulking. Cited formula, instant results in your browser, no signup. Estimates only, not medical advice.
Calculators for the everyday "how many calories should I eat?" and "how do I structure a cut or bulk?" questions, built around peer-reviewed formulas with the citations spelled out so you know exactly how the number was produced. The TDEE Calculator uses the Mifflin-St Jeor equation (1990) — the formula registered dietitians cite as more accurate than the older Harris-Benedict — and shows BMR alongside cut, maintain, and bulk targets in one card. Every calculation runs locally in your browser; your sex, age, height, and weight never leave your device. These tools provide population-level estimates with roughly ±10% accuracy and are not a substitute for individualized advice from a registered dietitian or physician.
The Health & Fitness Calculators Guide
How to use TDEE in a real diet plan
TDEE — Total Daily Energy Expenditure — is the calorie target that maintains your current weight. To lose fat, eat below it; to gain muscle, eat above it. The catch is that TDEE isn't fixed: it changes with bodyweight (less mass to maintain = lower BMR), with activity (skipping the gym for two weeks drops your real expenditure), and with diet history (chronic deficits trigger metabolic adaptation). The right workflow is: calculate TDEE, pick a deficit or surplus (a 500 kcal deficit projects roughly 0.45 kg / 1 lb of weight loss per week), eat at that calorie target for 14-21 days, weigh yourself daily, and look at the 14-day moving average. If your weight is moving faster or slower than expected, adjust your daily calories by 100-200 kcal and run another 14-day block. Recalculate TDEE every 4-6 weeks or every 5-10 lb of change.
Mifflin-St Jeor vs Harris-Benedict — which formula?
Most online calculators use one of three formulas. Harris-Benedict (1919, revised 1984) is the oldest and over-estimates BMR by 5-10% on modern populations because mid-20th-century body composition norms differed. Mifflin-St Jeor (1990) was developed specifically to correct that gap; it's the formula clinical dietitians and the American Dietetic Association recommend, and it's what this calculator uses. Katch-McArdle is the most accurate of the three but requires you to know your body fat percentage (it computes BMR from lean body mass, not total weight) — useful for athletes who've measured body fat with DEXA, less useful for most people who haven't. If you're not an athlete and don't have a DEXA scan, Mifflin-St Jeor is the right default and what registered dietitians use professionally.
Why these are estimates — and what to do about it
Population-level formulas can't account for individual variation. Two people with identical age, sex, height, and weight can have measured BMRs that differ by 10-15% due to thyroid function, muscle mass distribution, fidgeting (NEAT — Non-Exercise Activity Thermogenesis), and genetics. The formula gives you a starting point, not a verdict. The right move is to treat the calculator's TDEE as a hypothesis: eat at it for 14 days, weigh daily, and look at the trend. If your weight is stable, your real maintenance is exactly what the calculator said; if you're losing 1 lb/week without trying, your real TDEE is roughly 500 kcal higher; if you're gaining despite eating at the deficit, your real TDEE is lower. Adjust accordingly. Don't pile multiple formulas against each other — pick one and let measured weight change calibrate it.