How many calories to eat a day and how to work it out
How to estimate your daily calories with the Mifflin-St Jeor formula, what changes if you want to lose fat or build muscle, and why it's only an estimate.
There’s no magic number that works for everyone. What you need depends on your sex, age, height, weight and how much you move. But you can make a reasonable estimate in three steps.
1. Work out what your body burns at rest
The Mifflin-St Jeor formula, published in 1990, estimates the calories your body burns just by being alive:
- Men: 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5
- Women: 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161
A 30-year-old woman, 165 cm and 65 kg, comes out at about 1,370 kcal at rest.
2. Multiply by your activity level
The more you move, the more you burn. These are the usual factors:
| Activity | Factor |
|---|---|
| Little movement | × 1.2 |
| I walk every day | × 1.375 |
| I train 3-4 days | × 1.55 |
| I train almost daily | × 1.725 |
With the same example and daily walking: 1,370 × 1.375 ≈ 1,880 kcal. That’s your maintenance: at that amount, your weight stays roughly stable.
3. Adjust for your goal
- Maintain: eat your maintenance.
- Lose fat: a gentle deficit, for example 20% less, is easier to keep up than a sharp one.
- Build muscle: a small surplus, for example 10% more, along with enough protein and training.
Set a safety floor: eating very little for weeks isn’t a good idea. Kalo, for instance, never suggests less than 1,400 kcal for a woman or 1,600 for a man.
It’s an estimate
Two people with the same numbers can burn different amounts. Use the result as a starting point, log what you eat for a few weeks and watch how your weight changes: if it isn’t moving as you expected, adjust a little.
If you have a medical condition, are pregnant or breastfeeding, talk to a health professional before changing how you eat.
This guide is for information only and doesn’t replace the advice of a doctor or registered dietitian. For the broader picture of a healthy diet, see the WHO page.