How to use it· 4 steps
- Choose metric or imperial units, then enter your sex, age, height and weight. Add your body-fat percentage only if you have it from a reliable measurement.
- Pick the activity level that matches your planned exercise. If you are torn between two, choose the lower one.
- Choose a goal: maintain, or lose or gain at a weekly rate from 0.25 to 1 kg (0.5 to 2 lb).
- Read your daily target, maintenance calories and BMR with the working underneath, and compare all five activity levels in the table.
Step by step
How to use the calorie calculator
- 1Choose metric or imperial units, then enter your sex, age, height and weight. Add your body-fat percentage only if you have it from a reliable measurement.
- 2Pick the activity level that matches your planned exercise. If you are torn between two, choose the lower one.
- 3Choose a goal: maintain, or lose or gain at a weekly rate from 0.25 to 1 kg (0.5 to 2 lb).
- 4Read your daily target, maintenance calories and BMR with the working underneath, and compare all five activity levels in the table.
What the number is made of
Your daily energy use has three parts. Basal metabolic rate — the energy your organs use at complete rest, just to keep you alive — is the largest — for most people, well over half the day's total. Digesting food adds roughly another 10%. Movement makes up the rest — planned exercise plus everything else you do on your feet — and it is the part that varies most between people.
The calculator estimates the first part with an equation and folds the other two into one activity multiplier: total daily energy expenditure (TDEE) = BMR × activity factor. The factors are the conventional five — 1.2 sedentary, 1.375 lightly active, 1.55 moderately active, 1.725 very active and 1.9 extra active. They are a convention, not a measurement, which is why the table under the result shows all five.
Worked through for a 30-year-old man of 180 cm and 80 kg: Mifflin–St Jeor gives 10 × 80 + 6.25 × 180 − 5 × 30 + 5 = 1,780 kcal, and moderately active he maintains his weight on 1,780 × 1.55 = 2,759 kcal a day. A woman of the same age and size has −161 in place of +5, so a BMR of 1,614 kcal and maintenance of 2,502 kcal.
Choosing your activity level honestly
The multiplier moves the answer more than anything else you enter. Between sedentary and very active, the same person's maintenance figure differs by more than 40%, so an optimistic choice can erase a planned deficit entirely.
People reliably overestimate it. Moderately active means moderate exercise or sport three to five days a week — not a busy job or a day on your feet in an office. A desk job with three gym sessions a week usually sits nearer lightly active, because the other 23 hours of each day are sedentary.
Fitness trackers do not settle it: independent tests of popular wrist-worn devices have found their calorie estimates off by 20% or more, even when their heart-rate readings were good. When in doubt, take the lower level and let the scale tell you whether to move up.
How a weekly rate becomes a daily number
To lose weight you eat below maintenance; to gain, above it. The calculator converts the rate you choose using the long-standing approximation that a kilogram of body weight is worth about 7,700 kcal — the familiar 3,500 kcal per pound. Losing 0.5 kg a week therefore means 0.5 × 7,700 ÷ 7 = 550 kcal a day below maintenance, which takes the man above to about 2,209 kcal. Losing 1 lb a week means 500 kcal a day.
It is an approximation, and it errs in a known direction. As you lose weight your body needs less energy — there is less of you to move and maintain — so a fixed deficit produces less loss each month than it did in the first. Water and stored carbohydrate lost early on also make the first weeks look faster than the fat loss underneath. Dynamic models of weight change, such as Kevin Hall's at the US National Institutes of Health, predict a curve that flattens rather than the straight line the rule implies.
The consequence: recalculate every 4–5 kg (about 10 lb) using your new weight, and expect progress to slow before it stops. A plateau after months of steady loss is usually the arithmetic catching up, not a broken metabolism.
Low targets: why the tool warns instead of clamping
If your target falls below about 1,200 kcal a day for women or 1,500 kcal for men — the floors commonly cited for dieting without medical supervision — or below your own BMR, the calculator says so plainly. It does not quietly raise the number, because you asked for a rate and should see what it costs. Very low intakes make it hard to get enough protein, vitamins and minerals from food, and very fast losses tend to take more muscle with them.
Smaller people reach those floors sooner. A sedentary 30-year-old woman of 155 cm and 52 kg maintains her weight on roughly 1,410 kcal a day, so a 0.5 kg-a-week deficit would take her to about 860 kcal. Her better route is a slower rate plus more movement: lightly active, she maintains on about 1,620 kcal, and losing 0.25 kg a week keeps her above 1,300.
Gaining has the opposite risk: a surplus larger than your body can turn into muscle is stored as fat, so lean-gain guidance generally suggests a few hundred calories a day over maintenance, with resistance training, rather than the fastest rate on the menu.
Making the estimate yours
Every equation here predicts the average for people with your measurements. For most adults the best of them land within about 10% of a laboratory measurement, but some people sit well outside that, so treat the first target as a starting point.
Then calibrate. Eat close to the target for two to three weeks, weigh yourself a few mornings a week under the same conditions, and compare the trend with the plan. Losing faster than planned? Add 100–200 kcal a day. Slower? Take off the same. Your own data then replaces the equation's assumptions.
This calculator gives estimates for healthy adults, not medical or dietary advice. It is not designed for pregnancy or breastfeeding, for anyone under 18, or for people managing a medical condition, an eating disorder or medication that affects weight — in those situations a doctor or registered dietitian should set the numbers.
Answers
Frequently asked questions
How many calories should I eat to lose weight?
Subtract the deficit for your chosen rate from your maintenance figure (TDEE). At 0.5 kg (about 1 lb) a week that is roughly 550 kcal a day — around 2,200 kcal for a moderately active 80 kg man of 180 cm. The calculator warns if your target falls below the commonly cited floors.
Which formula is the most accurate?
For most adults, Mifflin–St Jeor: a 2005 systematic review for the American Dietetic Association found it the most reliable of the common equations. If you know your body fat from a decent measurement, Katch–McArdle can do better for very muscular people.
Why am I losing weight more slowly than the calculator predicted?
The 7,700 kcal per kg rule overstates loss over time, because a lighter body needs less energy. Underestimating food and overestimating activity are the other usual causes. Recalculate with your current weight, and adjust by 100–200 kcal if the trend stays off.
Should I eat back the calories I burn exercising?
Not if your activity level already includes that exercise — that would count it twice. The multiplier covers your typical week, training included.
Is anything I enter stored or uploaded?
No. The calculation runs in your browser, and nothing you type leaves the page.