How it's calculated
Your daily calorie needs are estimated in two steps:
- Basal metabolic rate (BMR): the calories your body uses at rest, from your sex, age, height and weight. The default is the Mifflin–St Jeor equation, published in 1990 from indirect-calorimetry measurements of 498 healthy adults aged 19 to 78.Am J Clin Nutr You can switch to the Harris–Benedict equations as revised by Roza and Shizgal in 1984.Am J Clin Nutr
- Total daily energy expenditure (TDEE): BMR multiplied by a physical activity level (PAL). The activity levels and their values come from the FAO/WHO/UNU expert report on human energy requirements.FAO/WHO/UNU
The weight-loss targets subtract 500 and 1,000 calories a day from maintenance. NHLBI's guidance is that a reduction of 500 to 1,000 calories a day produces a weight loss of about 1 to 2 pounds a week.NIH / NHLBI
These are estimates for planning, not medical advice.
The formula
Mifflin–St Jeor (weight in kg, height in cm, age in years):
- Men: BMR = 10 × weight + 6.25 × height − 5 × age + 5
- Women: BMR = 10 × weight + 6.25 × height − 5 × age − 161
Harris–Benedict, revised by Roza and Shizgal:
- Men: BMR = 88.362 + 13.397 × weight + 4.799 × height − 5.677 × age
- Women: BMR = 447.593 + 9.247 × weight + 3.098 × height − 4.330 × age
Activity (FAO/WHO/UNU):
| Lifestyle | PAL range | Value used |
|---|---|---|
| Sedentary or light activity | 1.40–1.69 | 1.53 |
| Active or moderately active | 1.70–1.99 | 1.76 |
| Vigorous or vigorously active | 2.00–2.40 | 2.25 |
The value used for each lifestyle is the mean PAL of the report's own worked daily-activity example for that lifestyle. You can enter a custom PAL anywhere in the report's 1.40–2.40 range.
Maintenance = BMR × PAL. Weight-loss targets = maintenance − 500 (about 1 lb a week) and maintenance − 1,000 (about 2 lb a week).
Worked example
A 35-year-old woman, 5 ft 5 in and 150 lb, with a desk job: her Mifflin–St Jeor BMR is 1,376 calories, and at a PAL of 1.53 she needs about 2,106 a day to keep her weight steady. Eating about 1,606 a day would be expected to lose about 1 pound a week.
Calories to maintain your weight: 3,133 CALORIES A DAY (ESTIMATE)
Assumptions and limitations
- Equations predict averages. Two people with the same age, size and activity can burn noticeably different amounts. Roza and Shizgal put the precision of the Harris–Benedict equations at about ±14% for normally nourished people, and the Mifflin paper found the original 1919 Harris–Benedict equations overestimated measured resting energy by about 5%.
- The PAL values were set for populations. The FAO/WHO/UNU report classifies the habitual activity of groups, and it calculates PAL against BMR from its own equations. Applying those multipliers to an individual's Mifflin–St Jeor BMR is a reasonable approximation, not a measurement.
- Rate of weight loss. CDC notes that people who lose weight gradually, about 1 to 2 pounds a week, are more likely to keep it off.CDC NHLBI found that this rate commonly lasts for up to 6 months, after which weight loss slows because the body uses less energy at the lower weight.NIH / NHLBI
- Calorie floors. NHLBI suggests 1,000–1,200 calories a day for most women and 1,200–1,600 for men on a weight-loss diet, and says diets under 800 calories a day should not be used routinely. The calculator flags any target below those levels.
- No weight-gain targets. We have not found an agency guideline that sets a calorie surplus for gaining weight, so the page doesn't suggest one.
- Adults only, not for pregnancy. Energy needs during pregnancy, breastfeeding, growth and illness are different. Ask a doctor or registered dietitian.
To split your calories into protein, carbohydrate and fat, use the macro calculator. Our guide to BMI, calories and macros explains how the numbers fit together.