Estimates only, not medical advice. These are population formulas, and any one person can be well above or below them. If you are pregnant or breastfeeding, under 18, have diabetes, kidney disease, an eating disorder or another medical condition, or take medicine that affects weight, talk to your doctor or a registered dietitian before changing how you eat.
How the calculator works
It takes three steps. First it estimates the calories your body burns at complete rest, your basal metabolic rate (BMR), with the Mifflin-St Jeor equation (1990). Then it multiplies by an activity factor to get the calories you burn on a normal day, your maintenance calories. Last, it adds or takes away calories for your goal, using the old rule that a pound of body weight is roughly 3,500 calories, so 500 calories a day is about 1 lb a week.
BMR (women) = 10 × weight in kg + 6.25 × height in cm − 5 × age − 161
BMR (men) = 10 × weight in kg + 6.25 × height in cm − 5 × age + 5
Maintenance = BMR × activity factor (1.2 to 1.9)
Daily calories = maintenance ± 500 × pounds per week
We use Mifflin-St Jeor because a 2005 systematic review by Frankenfield and colleagues found it predicted resting calories within 10% of the measured value for more people than the other common equations. The TDEE calculator shows two other formulas side by side if you want to compare.
Worked example: a 35-year-old woman, 5 ft 5 in, 165 lb
165 lb is 74.84 kg and 5 ft 5 in is 165.1 cm. Her BMR is 10 × 74.84 + 6.25 × 165.1 − 5 × 35 − 161 = 748.4 + 1,031.9 − 175 − 161 = 1,444 calories. She exercises 3 to 5 days a week, so her maintenance is 1,444 × 1.55 = 2,239 calories. To lose about 1 lb a week she would eat 2,239 − 500 = 1,739 calories a day. Losing 2 lb a week would mean 1,239 calories, only just above the 1,200 floor, which is a sign that 1 lb a week is the more realistic pace for her. Her BMI is 27.5. This example is loaded when the page opens.
The activity levels
The five multipliers (1.2, 1.375, 1.55, 1.725 and 1.9) are a long-standing convention used by most calorie calculators. We could not find a single original study for them. They do sit inside the physical activity level bands in the Institute of Medicine's dietary reference intakes, which run from about 1.0–1.39 for sedentary people to 1.9–2.49 for very active people (table reproduced in BMC Public Health). Most people overestimate how active they are, so if you are unsure, pick the lower level.
The safety floor
The CDC says people who lose weight gradually, about 1 to 2 lb a week, are more likely to keep it off. The 2013 AHA/ACC/TOS guideline on overweight and obesity suggests weight-loss diets of 1,200 to 1,500 calories a day for women and 1,500 to 1,800 for men. So the calculator never shows a loss target under 1,200 calories for women or 1,500 for men. When your goal would go lower, it shows the floor and the slower weekly loss it really gives.
Limits of any calorie estimate
- The formulas were built on groups of adults. Your real needs can be 10% or more above or below the estimate.
- As you lose weight, you burn fewer calories, so progress slows. Re-enter your new weight every 10 lb or so. The NIH Body Weight Planner models this slowdown over months.
- The calculator is for adults 18 and over. It does not cover pregnancy, breastfeeding, or teens who are still growing.
- Calories are not the whole story. The macro calculator splits your target into protein, carbs and fat.
Sources checked October 2026.
Questions people ask
How many calories should I eat a day?
It depends on your size, age, sex and how active you are. The Dietary Guidelines for Americans 2020–2025 estimate about 1,600 to 2,400 calories a day for adult women and 2,000 to 3,000 for adult men. This calculator narrows that down with the Mifflin-St Jeor formula and your activity level, then adds or takes away calories for your goal.
How many calories should I eat to lose weight?
A common starting point is about 500 calories a day below your maintenance level, which works out to roughly 1 lb a week. The CDC says people who lose about 1 to 2 lb a week are more likely to keep it off. We don’t show targets under 1,200 calories a day for women or 1,500 for men, the low ends of the 2013 AHA/ACC/TOS ranges. That floor is our conservative choice; the guideline itself reserves diets under 800 calories a day for medically supervised programs.
Why does the calculator stop at 1,200 or 1,500 calories?
The 2013 AHA/ACC/TOS obesity guideline suggests 1,200 to 1,500 calories a day for women and 1,500 to 1,800 for men as weight-loss diets. We don’t show targets under the low ends of those ranges. That is our conservative choice; the guideline itself reserves diets under 800 calories a day for medically supervised programs. If your goal would take you under the floor, the calculator shows the floor and the slower weekly loss it gives.
Is 1 lb of fat really 3,500 calories?
It is a rough rule that works for the first few weeks. As you lose weight your body burns a little less, so the same calorie cut gives slower loss over months. The NIH Body Weight Planner models that slowdown. Treat the weekly rate here as a starting estimate and re-check every 2 to 3 weeks.
How accurate is this calorie calculator?
A 2005 review in the Journal of the American Dietetic Association found Mifflin-St Jeor came within 10% of measured resting calories for more people than the other common equations, but not for everyone. Activity factors add more error. Use the number as a starting point, weigh yourself at the same time each week, and adjust by 100 to 200 calories if your weight is not moving as expected.
What if I want to gain weight or build muscle?
Choose a gain goal. Half a pound a week adds about 250 calories a day to maintenance, and 1 lb a week adds about 500. Slower gains, together with strength training and enough protein, tend to add more muscle and less fat. The protein calculator gives a daily target in grams.