BMR and TDEE, explained
Your body uses energy all the time, even asleep, to keep your heart beating, breathe and maintain body temperature. That baseline is your basal metabolic rate (BMR). It's usually 60–70% of the calories you use each day.
Add the energy you use moving around, exercising and digesting food, and you get your total daily energy expenditure (TDEE). That's the "maintain" number above: eat about this much and your weight should stay roughly steady.
How this calculator works
It uses the Mifflin-St Jeor equation (1990), which dietitians widely use because research has found it to be among the more accurate formulas for most adults.
Men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5
Women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161
BMR is then multiplied by an activity factor to estimate TDEE:
| Activity level | Multiply BMR by |
|---|---|
| Mostly sitting, little exercise | 1.2 |
| Light exercise 1–3 days a week | 1.375 |
| Moderate exercise 3–5 days a week | 1.55 |
| Hard exercise 6–7 days a week | 1.725 |
| Very hard exercise or a physical job | 1.9 |
Example: a 30-year-old woman, 165 cm, 65 kg, light exercise.
BMR = 650 + 1,031.25 − 150 − 161 = 1,370 calories.
TDEE = 1,370 × 1.375 = 1,884 calories a day to maintain her weight.
The weight-loss and gain numbers
A common rule of thumb is that a daily shortfall of about 500 calories leads to losing roughly 0.5 kg (1 lb) a week, and a surplus of 500 leads to a similar gain. In practice, results slow down over time because your body uses less energy as you get lighter. Treat these numbers as a starting point and adjust based on what actually happens over a few weeks.
Gradual change of 0.25–0.5 kg a week is generally considered sustainable. Very low intakes, below about 1,200 calories for women or 1,500 for men, make it hard to get enough nutrients and are best done only with medical supervision.
Why your real number may differ
- Body composition: people with more muscle burn more at rest than the formula expects.
- Activity is hard to judge: most people overestimate how active they are. If unsure, pick the lower level.
- Health conditions and medicines: thyroid conditions and some medicines change metabolism.
- Individual variation: even formula-matched people can differ by around 10% or more.
These numbers are estimates for healthy adults, not medical or nutrition advice. If you're pregnant, breastfeeding, under 18, managing a health condition, or have a history of disordered eating, please get guidance from a doctor or registered dietitian.
Frequently asked questions
Should I eat below my BMR to lose weight faster?
That's generally not recommended without medical supervision. Very low intakes can cost muscle, leave you short of nutrients and are hard to keep up.
Do calories from exercise count?
Your activity level already includes typical exercise. If you pick an active level, don't also "eat back" the calories your fitness tracker reports, or you'll count them twice.
How does this relate to BMI?
BMI tells you where your weight sits for your height; this tells you how much energy you use. The BMI calculator also shows a healthy weight range for your height.
Last reviewed November 2026.