How Many Calories Do You Need? BMR, TDEE and Deficits

Your body burns calories all day, even while you sleep. How many you need depends on your size, age, sex and how much you move. Once you can estimate that number, called your maintenance calories, you can plan to hold your weight, lose some or gain some. This guide shows how the estimate is made, with a worked example, and how to use it sensibly.

Step 1: Your basal metabolic rate (BMR)

BMR is the energy your body needs to stay alive at rest: breathing, circulation, temperature control and cell repair. The Mifflin-St Jeor equation, published in 1990 and widely used by dietitians, estimates it from weight, height and age:

Take a 25-year-old man who is 5 ft 10 in (177.8 cm) and weighs 165 lb (74.8 kg).

1. Weight term: 10 × 74.8 = 748.
2. Height term: 6.25 × 177.8 = 1111.
3. Age term: 5 × 25 = 125, which is subtracted.
4. Add 5 for a man: 748 + 1111 − 125 + 5 = 1,740 calories a day.

A woman with the same height, weight and age works out to about 1,574 calories, because the equation subtracts 161 instead of adding 5, a difference of 166.

Step 2: Add your activity (TDEE)

Your total daily energy expenditure, or TDEE, is BMR multiplied by an activity factor. Calculators vary slightly in the exact multipliers. These are the ones used on this site:

View the maintenance calories as numbers

Activity level	Multiplier	Calories per day
Sedentary (little or no exercise)	1.2	2,088
Light (exercise 1-3 times a week)	1.375	2,392
Moderate (exercise 4-5 times a week)	1.465	2,549
Active (daily or intense exercise 3-4 times a week)	1.55	2,696
Very active (intense exercise 6-7 times a week)	1.725	3,001
Extra active (very intense exercise daily, or a physical job)	1.9	3,305

The hard part is choosing the right row. People tend to overestimate their activity, so if you are unsure, pick the lower one. Use our TDEE Calculator or Calorie Calculator to do the arithmetic for you.

Step 3: Choose a goal

Eating at your TDEE roughly holds your weight steady. To lose weight you eat less than you burn, and to gain you eat more. A pound of body fat stores roughly 3,500 calories of energy, so a daily change of 500 calories adds up to about a pound a week. The example man at a moderate activity level needs about 2,549 calories to maintain, so a 500 calorie deficit means about 2,049.

Why real weight loss slows down

The 3,500 calorie rule assumes your burn stays the same while you lose weight, but it does not. A lighter body needs less energy, so the gap between what you eat and what you burn narrows over time. The chart below recalculates the example man's burn every week as his weight falls (the solid lines) and compares it with the simple straight-line prediction (the dashed line).

For a research-based projection, the National Institute of Diabetes and Digestive and Kidney Diseases offers a free Body Weight Planner that models these changes.

How low is too low?

Bigger deficits lose weight faster on paper, but they also increase the chance of muscle loss, tiredness and nutrient gaps. Commonly cited guidance is not to go below about 1,200 calories a day for women or 1,500 for men unless a doctor or dietitian is supervising, and many people need more than that. Gradual loss of around one to two pounds a week at most is the usual recommendation, and less is perfectly reasonable.

Getting more out of the number

• Track for two to three weeks, then compare your actual weight trend with the estimate and adjust by 100 to 200 calories if it is off.
• Weigh yourself under the same conditions, and look at weekly averages, because day-to-day water changes can hide real progress.
• Protein and strength training help preserve muscle while you lose fat.
• Small steps count: walking more raises the activity side of the equation without requiring harder diets.
• Recalculate when your weight, age or routine changes by a meaningful amount.

Common questions

Sources and further reading

• NIDDK: Body Weight Planner
• NHLBI: Calories and weight
• Dietary Guidelines for Americans
• Mifflin MD et al. (1990). A new predictive equation for resting energy expenditure. Am J Clin Nutr.

This guide is for general education and is not medical or dietary advice. Calorie estimates are approximate and individuals vary widely. Talk to a doctor or registered dietitian before making major changes to how you eat.