How many calories do you need?
Your body burns energy all day: to keep you alive at rest, to digest food and to move. The number of calories that matches all of that is your maintenance level. Eat about that much and your weight tends to stay steady; eat a little less or a little more over time and it tends to drift down or up.
This calorie calculator estimates your maintenance level from your sex, age, height, weight and how active you are. It then shows gentle targets for losing or gaining weight, and never suggests fewer than 1,000 calories a day.
Using the calculator
- Choose metric or US units.
- Pick your sex and enter your age, height and weight.
- Choose the activity level that matches a typical week, not your best one.
- Read the calories that keep your weight steady, then the targets for gentle loss or gain below it.
How the estimate is worked out
BMR (women) = 10 × kg + 6.25 × cm − 5 × age − 161
BMR (men) = 10 × kg + 6.25 × cm − 5 × age + 5
daily calories = BMR × activity factorThe first step is your basal metabolic rate (BMR), the energy you use at complete rest. It comes from the Mifflin-St Jeor equation, published in 1990 from measurements of 498 healthy adults, and widely used since. The second step multiplies BMR by an activity factor, from 1.2 for little exercise to 1.9 for very hard daily exercise or a physical job.
Worked example
A 35 year old woman is 165 cm tall, weighs 68 kg and exercises moderately three to five days a week.
- BMR: 10 × 68 + 6.25 × 165 − 5 × 35 − 161 = 1,375.25, about 1,375 calories
- Daily calories: 1,375.25 × 1.55 = 2,131.6, about 2,132 calories
- A gentle loss target, 500 fewer a day: 1,632 calories
About 2,132 calories a day would keep her weight roughly steady. Eating 250 or 500 fewer a day is a common, gentle way to lose weight; eating 250 or 500 more is a gentle way to gain.
Activity levels
| Activity level | Factor | Typical week |
|---|---|---|
| Little or no exercise | 1.2 | Desk job, little walking |
| Light | 1.375 | Light exercise 1 to 3 days |
| Moderate | 1.55 | Moderate exercise 3 to 5 days |
| Hard | 1.725 | Hard exercise 6 to 7 days |
| Very hard | 1.9 | Hard daily training or a physical job |
Most people overestimate how active they are. If you are unsure between two levels, pick the lower one and adjust after a few weeks.
Keeping it realistic
- Treat the number as a starting point. Real needs vary from person to person by a few hundred calories.
- Watch the trend, not the scale each morning. Weigh yourself at the same time of day and look at the change over a few weeks.
- Expect your needs to change as your weight changes. Recalculate after any big change.
- Go slowly. The NIH Body Weight Planner models how the body adapts to fewer calories, and it will not suggest under 1,000 calories a day either.
Frequently asked questions
How many calories should I eat a day?
It depends on your size, age, sex and how active you are, so two adults can need very different amounts: from well under 2,000 to over 3,000 calories a day. Enter your details above for a personal estimate, then watch how your weight responds over a few weeks and adjust.
What are maintenance calories?
Maintenance calories are the number of calories a day that keeps your weight about the same. It is your resting energy use, or BMR, scaled up for daily activity. Eating below it tends to lead to weight loss over time; eating above it tends to lead to weight gain.
How many calories should I eat to lose weight?
A common, gentle approach is to eat about 250 to 500 calories a day fewer than your maintenance level. The calculator shows both targets. It will not show a target under 1,000 calories a day, and it flags any target below your BMR, because very low intakes need a doctor’s guidance.
How accurate is a calorie calculator?
It gives a good estimate for most healthy adults, but not an exact figure. Studies comparing the Mifflin-St Jeor equation with measured energy use find it among the most reliable of the common equations, while still missing by a meaningful amount for some people. Your own weight trend is the best check.
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