Overview
What this tool does
TDEE (Total Daily Energy Expenditure) is the number of calories your body burns in a day at your current activity level. It's the baseline for any calorie-tracking goal: eat less than your TDEE to lose weight, more to gain. This calculator uses the Mifflin-St Jeor BMR formula (the most accurate of the widely-used formulas) and multiplies by your activity level to get TDEE. It also gives you 5 calorie targets ranging from aggressive cut (-1 lb/wk) to aggressive bulk (+1 lb/wk). Pure math, runs entirely in your browser.
How to
Use it in 3 steps
- Pick metric or imperial units, then your biological sex (the Mifflin-St Jeor formula uses different constants).
- Enter age, height, and weight.
- Pick your activity level. Be honest. Most people overestimate; if you have a desk job and exercise 3x a week, pick 'lightly active' or 'moderately active', not 'very active'.
- Read BMR (calories burned at rest) and TDEE (calories burned at your activity level).
- Pick a goal target from the 5 below. Track your weight for 2-3 weeks at that target, then adjust.
FAQ
Frequently asked questions
▶What's the difference between BMR and TDEE?
BMR (Basal Metabolic Rate) is what you'd burn if you stayed in bed all day. TDEE is what you actually burn, which adds the calories spent on walking, standing, exercising, and digestion. Most weight-loss math is anchored to TDEE, not BMR.
▶Why Mifflin-St Jeor and not Harris-Benedict?
Mifflin-St Jeor was published in 1990 with a larger and more diverse dataset than the original 1919 Harris-Benedict equation. Multiple studies have shown it's more accurate for modern populations. Both are 'good enough' estimates; neither replaces a metabolic-cart measurement.
▶I picked 'moderately active' but I'm still gaining weight at TDEE.
Two common reasons: you're overestimating activity, or you're under-tracking calories. People consistently log 20-30% fewer calories than they actually eat, especially weekends and dining out. Try one level down on activity, log meticulously for 2 weeks, then adjust.
▶Why does the 'aggressive cut' target use -500 cal/day?
There's roughly 3,500 calories in a pound of body fat (long-standing rule of thumb; the actual number varies a bit). 500 cal/day x 7 days = 3,500 cal = ~1 pound per week. Faster than that is harder to sustain and more likely to lose muscle alongside fat.
▶Is my data sent anywhere?
No. Math runs in your browser. Age / sex / height / weight stay on your device.
▶Does this work for very athletic people or people with PCOS / thyroid issues?
Mifflin-St Jeor assumes average body composition. Very high-muscle individuals (bodybuilders, elite athletes) may need to add 100-200 cal to TDEE. People with thyroid disorders, PCOS, or certain medications often have BMR that's noticeably off the formula prediction. Use the number as a starting point and adjust based on real-world weight change over 2-4 weeks.