How the calculation works
The calculator uses the Mifflin-St Jeor equation, which studies have found to be the most accurate simple formula for estimating resting energy use in adults:
| Activity level | Factor |
|---|---|
| Sedentary: desk job, little exercise | 1.2 |
| Lightly active: exercise 1–3 days a week | 1.375 |
| Moderately active: 3–5 days a week | 1.55 |
| Very active: 6–7 days a week | 1.725 |
| Extremely active: physical job plus training | 1.9 |
Calories for weight loss
A kilogram of body fat stores roughly 7,700 kcal (about 3,500 kcal per pound). Eating 550 kcal a day below maintenance adds up to about 0.5 kg a week. Faster loss needs bigger deficits, which are harder to sustain and risk losing muscle. Most guidelines recommend aiming for 0.5–1 kg (1–2 lb) a week at most.
The calculator won't suggest less than 1,200 kcal a day for women or 1,500 for men, the levels below which it becomes hard to meet nutritional needs without medical supervision.
Why your real number may differ
- Equations predict the average; individuals vary by around 10% either way.
- People often overestimate their activity level. If unsure, choose the lower option.
- Muscle burns more energy than fat, so very muscular people need more.
- Metabolism adapts as you lose weight, so recalculate every 4–5 kg.
The best test is real life: track your intake and weight for two to three weeks and adjust by 100–200 kcal if your weight isn't moving as expected.
Calories aren't everything
For health, what you eat matters as well as how much. Plenty of protein helps you keep muscle while losing weight; fibre from vegetables, fruit and whole grains keeps you full. Use the Macro Calculator to split your calories into protein, carbs and fat.
Frequently asked questions
How many calories should I eat a day?
It depends on your sex, age, height, weight and activity. Most adult women need roughly 1,800–2,400 kcal and men 2,200–3,000 kcal to maintain weight. Enter your details for a personal estimate.
How many calories should I eat to lose weight?
About 500–550 kcal a day below your maintenance level to lose roughly 0.5 kg (1 lb) a week.
What is TDEE?
Total daily energy expenditure: the calories you burn in a day, including resting metabolism, daily activity, exercise and digestion.
Which formula does this calculator use?
The Mifflin-St Jeor equation, multiplied by a standard activity factor.
Is a 1,200 calorie diet safe?
1,200 kcal is generally the lowest level recommended for women without medical supervision. Many people need more to stay healthy.
Last updated October 2026 · More health & fitness calculators