How your calories are calculated
We use the Mifflin–St Jeor equation — the formula most dietitians and the NHS regard as the most accurate for estimating resting metabolism:
(s = +5 for men, −161 for women)
Your BMR is the energy you'd burn at complete rest. Multiplying it by an activity factor (1.2 sedentary → 1.9 athlete) gives your TDEE — total daily energy expenditure, or your maintenance calories. To lose weight we subtract ~500 kcal/day (about 0.5 kg/week); to gain we add ~300 kcal/day.
What the numbers mean
- BMR — baseline calories to keep your body running at rest.
- Maintenance (TDEE) — eat this to stay the same weight.
- Target — your goal-adjusted daily calories.
The ring shows a common starting macro split (30% protein / 40% carbs / 30% fat). Protein and carbs are 4 kcal per gram, fat is 9 — adjust to your own preference and any advice from a professional.
What is TDEE?
TDEE (Total Daily Energy Expenditure) is the total calories you burn in a day — your BMR plus everything you do. Eating at your TDEE maintains your weight.
How many calories to lose weight?
A deficit of about 500 kcal/day typically loses ~0.5 kg (1 lb) per week — a safe, sustainable pace. This tool sets that automatically when you choose "Lose".
Is Mifflin–St Jeor accurate?
It's the most accurate widely-used prediction equation for most people, but every estimate has a margin. Track your weight over 2–3 weeks and adjust intake if it isn't moving as expected.
Why does activity level matter so much?
Movement is a big share of daily burn. Going from sedentary (×1.2) to active (×1.725) can add hundreds of calories to your maintenance figure — be honest for a realistic number.
Is this private?
Yes — it runs entirely in your browser. Nothing you enter is uploaded or stored.
- Mifflin MD, St Jeor ST, et al. — A new predictive equation for resting energy expenditure (1990)
- NHS — Healthy weight & calorie guidance
Evidence-based · last reviewed July 2026