Calorie Calculator

Your body burns energy around the clock, most of it simply keeping you alive rather than moving you around. This calculator estimates two numbers that describe that: your basal metabolic rate, what you would burn lying still all day, and your total daily energy expenditure, that baseline scaled up for how active you are. It then shows what those figures mean for losing, maintaining or gaining weight.

BMR and TDEE: what the two numbers mean

Your basal metabolic rate (BMR) is the energy your body uses at complete rest to run your brain, heart, lungs and everything else. For most people it is the largest share of daily energy use, which is why two people of the same weight can have different needs before either does any exercise.

Your total daily energy expenditure (TDEE) is BMR multiplied by an activity factor, and it is the number that matters for planning. Eat around your TDEE and your weight tends to hold steady over time.

The Mifflin-St Jeor equation

This tool uses the Mifflin-St Jeor equation, published in 1990, which is the resting-energy formula most commonly recommended for healthy adults today. It takes weight in kilograms, height in centimetres and age in years:

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

The two versions differ only by a constant, so at identical height, weight and age the male figure is 166 kcal higher, and the negative age coefficient means the estimate falls by about 5 kcal per year of age. Mifflin-St Jeor largely replaced the older Harris-Benedict equation of 1918, which tended to overestimate resting needs in modern populations. Neither considers body composition, their shared blind spot.

Activity multipliers and how to choose one

Your BMR is multiplied by one of five factors to reach TDEE:

• 1.2 – Sedentary: little or no exercise, mostly seated day
• 1.375 – Light: exercise 1 to 3 days a week
• 1.55 – Moderate: exercise 3 to 5 days a week
• 1.725 – Active: exercise 6 to 7 days a week
• 1.9 – Very active: intense daily training, or a physical job on top of training

This is the largest source of error in the result, and the steps are coarse: moving from 1.55 to 1.725 changes the answer by roughly a tenth. Most people overestimate, because the labels count structured workouts but say nothing about the other twenty-three hours. If you are unsure, pick the lower option and adjust after a few weeks of real-world results.

Reading the goal figures

The three coloured cards apply a flat 500 kcal adjustment either side of your TDEE. That comes from the long-standing rule of thumb that roughly 3,500 kcal corresponds to about a pound of body fat, so a 500 kcal daily gap works out at roughly a pound, a little under half a kilogram, per week.

Treat it as an approximation with known limits. Metabolism adapts as body mass changes, so a deficit that produces steady loss at the start typically produces less later, and progress tends to slow rather than continue in a straight line. The panel also shows your BMI and its category from the same height and weight, using the standard bands: under 18.5 underweight, 18.5 to 24.9 normal, 25 to 29.9 overweight, 30 or above obese. For the fuller picture, including a healthy weight range for your height, see the BMI Calculator.

Accuracy and limitations

• It is a prediction, not a measurement. Resting metabolism varies between individuals, so your true figure may sit above or below the number shown.
• Body composition is invisible to it. Lean tissue burns more at rest than fat, so a lean person and a less lean person of the same height, weight and age get the same estimate despite different real needs.
• Metric only. Height must be in centimetres and weight in kilograms, so convert first if you use feet and pounds.
• Some situations fall outside its scope, including pregnancy, breastfeeding, adolescent growth, and thyroid or metabolic conditions.

Once you have a calorie target, the split between protein, carbohydrate and fat is a separate question, which the Macro Nutrient Calculator covers.

How to use the Calorie Calculator

1. Select Male or Female at the top, since this changes the constant in the equation.
2. Enter your age in years (15 upwards), your height in centimetres and your weight in kilograms.
3. Pick the activity level that honestly matches a typical week, not your best week.
4. Read your TDEE in the large figure, with BMR, BMI and BMI category in the cards below. Everything updates as you type.
5. Compare the three goal cards, then re-run with a different activity level to see how sensitive the result is to that one choice.

Frequently Asked Questions

Which formula does this calculator use?

The Mifflin-St Jeor equation for BMR, with a separate constant for men and women, multiplied by one of five standard activity factors between 1.2 and 1.9 to give TDEE.

How accurate is the estimate?

Mifflin-St Jeor is well regarded for healthy adults, but every prediction equation carries individual variation and the activity multiplier adds more on top. Treat the result as a starting point: tracking your weight over two to three weeks tells you more than any formula can.

Should I eat below my BMR to lose weight faster?

Eating below your basal rate is not something to decide on your own. Very low intakes make it hard to meet nutrient needs and are generally used only under professional supervision. The deficit shown here is applied to TDEE, not BMR, for that reason.

Why is the 500 calorie adjustment the same for everyone?

Because it comes from a fixed rule of thumb rather than from your inputs. A 500 kcal gap is a larger proportion of a small TDEE than a large one, so it represents a gentler change for some people and a sharper one for others.

Do I need to recalculate as my weight changes?

Yes. Weight appears directly in the equation, so BMR and TDEE shift with it. Re-running the numbers after every few kilograms keeps the target realistic.

Does it store or send my details?

No. Everything is computed in your browser by JavaScript on this page. Your age, height, weight and activity level never leave your device, and nothing is retained after you close the tab.

Sources

• Mifflin MD, St Jeor ST and colleagues (1990) – "A new predictive equation for resting energy expenditure in healthy individuals", American Journal of Clinical Nutrition.
• Harris JA and Benedict FG (1918) – the earlier basal metabolism equation, referenced above for comparison only.
• FAO/WHO/UNU expert consultation on human energy requirements – the physical activity level (PAL) approach of multiplying resting expenditure by an activity factor.
• World Health Organization – adult BMI classification, used for the BMI category shown in the results panel.