How Many Calories Do I Need a Day?
There is no single right number. Your calorie needs depend on your size, age, sex and above all how much you move. You can estimate them reasonably well in two steps.
Step 1: basal metabolic rate (BMR)
BMR is the energy your body uses at rest to keep you alive. The most widely used formula today is the Mifflin-St Jeor equation. In metric units:
- Women: 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161
- Men: 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5
To use pounds and inches, multiply pounds by 0.4536 and inches by 2.54 first.
A 40-year-old man who is 5 ft 10 in (178 cm) and weighs 180 lb (81.6 kg) has a BMR of about 1,730 calories.
Step 2: total daily energy expenditure (TDEE)
Multiply BMR by an activity factor:
| 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 |
| Extra active (physical job or training twice a day) | 1.9 |
With moderate exercise, the man in the example needs about 2,690 calories a day to maintain his weight.
To lose weight
A deficit of about 500 calories a day typically leads to losing around 1 pound a week at first. Progress slows over time because a smaller body burns fewer calories.
Practical guidelines:
- Keep the deficit moderate, around 300 to 500 calories. Bigger cuts are hard to sustain and cost more muscle.
- Eat enough protein, which helps preserve muscle and keeps you full.
- Add strength training alongside cardio.
To gain weight
To build muscle, a small surplus of about 250 to 500 calories a day combined with strength training limits fat gain.
Why your real number may differ
The formula gives an average. Two people with identical stats can differ by several hundred calories a day because of body composition, everyday movement such as walking and standing, and genetics. The practical approach:
- Start with the estimate.
- Weigh yourself under the same conditions for two to three weeks.
- Adjust by 100 to 200 calories based on the trend.
When to get professional advice
During pregnancy or breastfeeding, for teenagers, with diabetes or other medical conditions, or if you have a history of disordered eating, calorie needs change. A doctor or registered dietitian can give you a safe target.
Results are estimates for informational purposes only and are not financial, tax, legal or medical advice.