How many calories do you need a day?
An adult usually needs 1,600–2,400 kcal a day (women) and 2,000–3,000 kcal a day (men), according to the Dietary Guidelines for Americans 2020–2025, depending on weight, height, age and how active they are.
The calculator first estimates your basal metabolic rate (the energy for basic functions at rest) with the Mifflin-St Jeor formula, then multiplies it by an activity factor between 1.2 and 1.9.
How are calorie needs calculated?
Daily calorie needs (TDEE) are your basal metabolic rate (BMR) multiplied by an activity factor. BMR is calculated with the Mifflin-St Jeor equation, published in 1990, which a 2005 systematic review (Frankenfield et al.) found to be the most accurate of the common formulas for healthy adults.
For targets, the calculator subtracts 500 kcal a day for weight loss (about 0.5 kg a week) or 250 kcal for slow weight loss, and adds 300 kcal for weight gain. The weight-loss target never goes below BMR.
Formula
- Women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) − 161
- Men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) + 5
- TDEE = BMR × activity factor (1.2 – 1.9)
Worked example
A 30-year-old woman, 165 cm and 65 kg, moderately active: BMR = 10 × 65 + 6.25 × 165 − 5 × 30 − 161 = 1,370 kcal. TDEE = 1,370 × 1.55 = 2,124 kcal a day. To lose about 0.5 kg a week, her target would be around 1,620 kcal a day; for maintenance, 2,120 kcal; for weight gain, 2,420 kcal.
Which activity factor should you choose?
| Level | What a week looks like | Factor |
|---|---|---|
| Sedentary | desk job, driving, no exercise | 1.2 |
| Lightly active | light exercise 1–3 days a week | 1.375 |
| Moderately active | exercise 3–5 days a week | 1.55 |
| Very active | hard exercise 6–7 days a week | 1.725 |
| Extremely active | heavy physical work or training twice a day | 1.9 |
What does the formula not know?
- It does not know how much muscle you have: it underestimates for very muscular people and may overestimate with obesity.
- The activity factor is chosen subjectively, and many people overestimate their activity. If in doubt, pick the level below.
- It is made for healthy adults; it does not apply to children, during pregnancy or breastfeeding, or with conditions that change metabolism (such as thyroid disease).
- The result is an average: your real needs may be about 10% higher or lower.
When should you talk to a specialist?
Talk to a doctor or dietitian if you have diabetes, kidney, heart or thyroid disease, if you are pregnant or breastfeeding, if you have had an eating disorder, or if the calculated target feels hard to stick to.
A specialist can measure your body composition and adjust the target based on how your body responds in the first weeks.
Working with a nutritionist? See how they follow you in Rod