Calorie Calculator

What this calculator does

This tool estimates how many calories you use in a day. It works in two steps: first it calculates your Basal Metabolic Rate (BMR), the energy your body burns at complete rest, then it multiplies that by an activity factor to produce your Total Daily Energy Expenditure (TDEE), often called maintenance calories. You enter your sex, age, height, weight and activity level in metric or imperial units, and the calculator shows your maintenance figure along with a small table of common deficit and surplus targets — 250 and 500 kilocalories below and above maintenance. Every number updates live as you adjust an input, and the maintenance figure can be copied with one click.

Why you might need it

A calorie estimate is the practical version of “how much energy do I need”. Resting metabolism alone does not answer that, because daily life adds the cost of walking, working and exercising. This calculator combines both into one figure. It is useful when setting up a nutrition-tracking app that asks for a starting calorie target, when reading food labels and wanting a sense of scale, or when comparing how different activity levels change daily energy needs. The deficit and surplus rows are convenient as plain reference points: they show, arithmetically, what a fixed change relative to maintenance looks like in calories, without you having to do the subtraction yourself.

How to use it

1. Choose Metric or Imperial with the units toggle.
2. Select your sex and enter your age in years.
3. Enter your height and weight — centimetres and kilograms in metric, feet plus inches and pounds in imperial.
4. Pick an activity level from sedentary through to extra active; each option shows its multiplier.
5. Read the maintenance calories result, and see the goal table for the deficit and surplus figures. Use Copy TDEE or Reset as needed.

How it’s calculated

The BMR step uses the Mifflin-St Jeor equation (Mifflin and St Jeor, 1990):

• Men: BMR = (10 × kg) + (6.25 × cm) − (5 × age) + 5
• Women: BMR = (10 × kg) + (6.25 × cm) − (5 × age) − 161

Imperial input is converted to metric first — height to centimetres, weight to kilograms — so the result does not depend on the unit system. The TDEE is then BMR multiplied by an activity factor: 1.2 sedentary, 1.375 lightly active, 1.55 moderately active, 1.725 very active, 1.9 extra active. The deficit and surplus rows simply add or subtract 250 and 500 kilocalories from the TDEE. The Harris-Benedict equation is an alternative basis for the BMR step — it predates Mifflin-St Jeor, uses the same four inputs with different coefficients, and the activity multipliers above were originally paired with it. Mifflin-St Jeor is used here because it generally tracks measured resting metabolism more closely for the modern population.

Common pitfalls

The biggest source of error is the activity factor, because it is a self-rated estimate. People frequently overestimate how active they are, which inflates the TDEE; if in doubt, choosing the lower of two adjacent levels gives a more conservative figure. Remember too that both the BMR equation and the multipliers are population averages — individual metabolism varies with body composition, genetics and hormones — so the maintenance number is a starting estimate, not an exact requirement. The “3,500 kcal per pound” idea behind the ±500 rows is a rough rule of thumb, not a precise physiological constant. And as always, check the units toggle before reading the result so height and weight are interpreted in the system you intend.

Tips and related calculations

If you want to see the resting baseline on its own, a BMR calculator reports just the first step of this calculation. A BMI calculator answers a different question entirely — how your weight compares with your height — and pairs well with this tool for a fuller picture. When you re-run the calorie estimate over time, keep weigh-ins consistent and update your weight as it changes, since TDEE shifts with body mass. Because the entire calculation, from the equation to the deficit arithmetic, runs locally in your browser, you can try different activity levels and inputs as often as you like with nothing ever transmitted.