Calorie Calculator

How many calories do you need each day?

Your body burns energy all day, even when you are lying still. That baseline is the basal metabolic rate (BMR). On top of it comes the energy you spend moving, from walking to the shop to training for a marathon, plus a small amount for digesting food. Add them together and you get the calories needed to keep your weight where it is, often called maintenance calories or total daily energy expenditure.

Eat more than that figure for long enough and the surplus is stored, mostly as body fat. Eat less and the body draws on its stores. This calculator estimates maintenance first, then shows what a steady surplus or deficit would look like.

Using the calculator

1. Pick US units or Metric units. The weekly targets are then shown in pounds or kilograms.
2. Enter your age in years, choose male or female, and fill in your height and weight. Check the unit selector beside your weight, because it decides whether the number is read as pounds or kilograms.
3. Choose the activity level that describes a typical week, not your most active day.
4. Press Calculate. The first line is your maintenance estimate, the four lines below it are the weight-change targets, and the last line is your BMR.

Age must be at least 1. Results are rounded to the nearest whole calorie.

The formula behind the numbers

The calculator estimates BMR with the Mifflin-St Jeor equation, published in 1990 and widely used by dietitians because it has held up well in later validation studies. Weight is in kilograms and height is in centimetres.

BMR (men) = 10 × weight + 6.25 × height − 5 × age + 5

BMR (women) = 10 × weight + 6.25 × height − 5 × age − 161

BMR is then multiplied by a factor that reflects how active you are. Maintenance calories = BMR × activity factor.

The weight-change targets add or subtract a fixed amount from the maintenance figure: 500 Calories a day for the smaller step and 1,000 Calories a day for the larger one, in both directions.

Worked example

A woman aged 25 is 165 cm tall, weighs 60 kg and exercises three to five times a week (moderate).

BMR = 10 × 60 + 6.25 × 165 − 5 × 25 − 161 = 1,345 Calories

Maintenance = 1,345.25 × 1.55 ≈ 2,085 Calories a day

To lose roughly half a kilogram a week she would aim for about 2,085 − 500 = 1,585 Calories a day, and to gain at the same pace about 2,585 Calories. Those are starting points. Track your weight over two to three weeks and adjust by 100 to 200 Calories if the trend is off.

Why 500 Calories a day is about a pound a week

A common rule of thumb says a pound of body fat holds about 3,500 Calories, or roughly 7,700 Calories per kilogram. A daily gap of 500 Calories therefore adds up to 3,500 over a week, which is why 500 maps to about a pound. The rule is an approximation: the body adapts as weight changes, water shifts mask fat loss for the first weeks, and some of the weight lost or gained is not fat.

Keep in mind that the calculator applies the same 500 and 1,000 Calorie steps to gaining. By the 3,500 rule those surpluses correspond to about 1 and 2 pounds a week, so the US-unit labels for gaining (0.5 and 1 pound) are on the generous side, and a surplus of 250 to 500 Calories is the more usual advice for gaining lean mass. Many health bodies suggest losing between half a kilogram and one kilogram (1 to 2 pounds) a week at most. Larger deficits are harder to sustain and increase the chance of losing muscle. The calculator does not enforce a minimum, so a small person on the bigger deficit can see a very low or even negative figure. Treat that as a sign the target is unrealistic, not a goal.

These results are estimates for general information, not medical or dietetic advice. Pregnancy, breastfeeding, illness, medication and eating disorders all change energy needs. Speak to a doctor or registered dietitian before making large changes to your diet. See the disclaimer.

What changes your calorie needs

• Body size. Larger bodies burn more energy at rest, so weight and height both raise BMR.
• Age. BMR falls slowly through adult life, partly because muscle mass declines. The equation subtracts 5 Calories for every year.
• Sex. On average men carry more lean mass than women of the same size, which is why the constants differ by 166 Calories.
• Body composition. Muscle burns more than fat at rest. Two people with identical height and weight can differ by a couple of hundred Calories a day. The lean body mass calculator and body fat calculator help you see the split.
• Activity and non-exercise movement. Job, steps and fidgeting often matter as much as workouts.
• Hormones, sleep and health. Thyroid conditions, poor sleep and some drugs shift energy use in ways no equation can capture.

The equation is an average fitted to groups of people. Individual metabolic rates scatter around it, commonly by 10 percent or more, so use the output as a first guess and let your own weight trend decide.

Turning the number into a plan

Calories are a unit of energy; one dietary Calorie (kcal) equals 4.184 kilojoules. Food labels let you add them up: carbohydrate and protein supply about 4 Calories per gram, fat about 9 and alcohol about 7. Weighing portions for a week or two is the quickest way to learn what your usual intake really is.

If you want a second opinion on the same inputs, the TDEE calculator and BMR calculator show maintenance and resting energy separately, and the weight loss calorie calculator plans a target date. To drink enough alongside your food, try the water intake calculator.