Calorie Calculator

What this does

So you are curious roughly how many calories your body uses in a day, as a starting point for thinking about food. This calculator gives you an estimate. From your weight, height, age, sex, and how active you are, it works out an approximate daily calorie figure: the energy it takes to maintain your current weight at that activity level.

How to use it

1. Enter your current weight, choosing pounds or kilos, along with your height in centimetres and your age.
2. Select your sex and your activity level.
3. Press Calculate to see your estimated calories per day.

How the maths works

The calculator uses the Mifflin-St Jeor equation, which is the most accurate of the widely used formulas for estimating your basal metabolic rate, or BMR, the energy your body burns at complete rest. It works from your weight in kilograms, height in centimetres, and age:

male BMR = (10 × kg) + (6.25 × cm) - (5 × age) + 5

female BMR = (10 × kg) + (6.25 × cm) - (5 × age) - 161

Your BMR is most of the story, usually around 60 to 75 percent of what you burn, but not all of it. To get your total for the day, the tool multiplies your BMR by an activity factor, somewhere between about 1.2 for very little exercise and 1.9 for a physically demanding life:

daily calories = BMR × activity factor

As an example, a 35 year old woman who weighs 68 kg and stands 165 cm tall has a BMR of about 1,375 calories. If she is lightly active, multiplying by 1.375 gives roughly 1,890 calories a day to maintain her weight.

What the number means

The figure you get is a maintenance estimate, the rough amount of energy that keeps your weight roughly steady at your current activity level. In broad terms, eating consistently below it tends to lead to weight loss over time, and eating above it tends to lead to weight gain. It is a baseline to understand your body, not a prescription, and it does not tell you what any particular goal should look like for you.

Accuracy and a note of caution

This is an estimate, not a measurement of your actual metabolism, and it comes with real limits. The accuracy tends to fall off at the extremes of body composition, after a large change in weight, or when illness or certain medications alter how your body uses energy. Two people with the same height, weight, and age can genuinely need different amounts.

So please treat the number gently. If you are thinking about changing what you eat for a specific goal, a doctor or a registered dietitian can give you guidance that fits your body, your health, and your life far better than any formula can, and that is especially worth doing before making big changes. Eating very few calories is not something to attempt without medical supervision. This tool is here for general interest and as a rough starting point, not as medical or dietary advice.

Questions people ask

References

1. Medscape Reference. Mifflin-St Jeor Equation. https://reference.medscape.com/calculator/846/mifflin-st-jeor-equation