Calorie Calculator
Losing weight starts with one number: how many calories you burn in a day. This calculator works out your BMR with the Mifflin-St Jeor equation from age, sex, height, and weight in metric or imperial units, multiplies it by your activity level for your TDEE (maintenance calories), then applies a daily deficit to give a calorie target, an estimated weekly loss, and an estimated date to reach your goal weight. Every figure shows its math, example values are labelled as examples, and all results are estimates only — not medical advice.
Switching units only changes how you enter height and weight — the calorie formula is the same either way.
Your age in years. BMR falls with age because the formula subtracts 5 kcal per year of age.
The Mifflin-St Jeor equation has a different constant for men (+5) and women (−161) at the same height, weight, and age.
Your height in centimetres. 1.80 m is 180 cm.
Your current weight in kilograms.
Be honest here — this is the biggest source of error. Most people overestimate their activity, which inflates the TDEE and shrinks the real deficit.
The weight you want to reach. The goal date counts the gap between this and your current weight at your chosen deficit.
A deficit is TDEE minus intake. 500 kcal a day is the classic "pound a week" level in imperial terms (3,500 kcal a week); in metric it works out to about 0.45 kg a week.
Daily calorie target
2,259kcal/day
- BMR10 × 80.0 + 6.25 × 180.0 − 5 × 30 + 5 = 1780.
- 1,780kcal/day
- TDEE (maintenance calories)1780 × 1.55 = 2759.
- 2,759kcal/day
- Daily target (with deficit)2759 − 500 = 2259.
- 2,259kcal/day
- Estimated weekly loss500 × 7 ÷ 7700 = 0.45 kg/week.
- 0.45kg/week
- Days to goal weight5.0 kg × 7700 ÷ 500 = 77 days.
- 77days
- To gain about 0.5 kg/week2759 + 500 = 3259.
- 3,259kcal/day
How it was calculated
- BMR (Mifflin-St Jeor, male): 10 × 80.0 + 6.25 × 180.0 − 5 × 30 + 5 = 1780 kcal/day.
- TDEE: 1780 × 1.55 (moderate activity) = 2759 kcal/day. This is your maintenance level — eating this much holds your weight steady.
- Daily target: 2759 − 500 deficit = 2259 kcal/day.
- Weekly change at this deficit: 500 × 7 ÷ 7700 = 0.45 kg per week.
- Goal date estimate: 5.0 kg to lose × 7700 ÷ 500 = 77 days (about 11.0 weeks) at this deficit every day. Real loss slows as you get lighter because your BMR and TDEE fall with your weight — treat the date as an estimate, not a promise.
- To gain about 0.5 kg a week instead: 2759 + 500 = 3259 kcal/day (the same 7,700 kcal-per-kilogram rule, run in reverse).
- Estimates only — not medical advice. BMR equations estimate an average; your real burn varies with muscle mass, hormones, sleep, and activity the factor cannot see.
How it works
BMR uses the Mifflin-St Jeor equation, the most widely validated resting-energy formula for adults. For men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5. For women the last term is − 161 instead of + 5. The brief example is a 30-year-old man at 80 kg and 180 cm: 10 × 80 + 6.25 × 180 − 5 × 30 + 5 = 800 + 1,125 − 150 + 5 = 1,780 kcal/day at rest.
TDEE (total daily energy expenditure) is BMR × an activity factor: sedentary 1.2, lightly active 1.375, moderately active 1.55, very active 1.725, extra active 1.9. The brief example at moderately active gives 1,780 × 1.55 = 2,759 kcal/day — that is maintenance, the intake that holds weight steady. A deficit subtracts from TDEE: 2,759 − 500 = 2,259 kcal/day as the target.
The goal date uses the 7,700 kcal-per-kilogram rule: a kilogram of body fat stores roughly 7,700 kcal, so a 500 kcal daily deficit loses about 500 × 7 ÷ 7,700 = 0.45 kg a week, and 5 kg takes 5 × 7,700 ÷ 500 = 77 days. Real loss is not linear — BMR and TDEE fall as you get lighter — so the date is an estimate, and the tool re-checks it every time you re-enter your current weight.
Worked examples
Brief example: 30-year-old man, 80 kg, 180 cm, moderately active → 2,259 kcal/day
Enter age 30, male, 180 cm, 80 kg, moderately active, goal 75 kg, 500 kcal deficit: BMR = 10 × 80 + 6.25 × 180 − 5 × 30 + 5 = 1,780, TDEE = 1,780 × 1.55 = 2,759, so the daily target is 2,759 − 500 = 2,259 kcal/day. That deficit loses about 0.45 kg a week, and the 5 kg gap to 75 kg takes 5 × 7,700 ÷ 500 = 77 days — about 11 weeks — if the deficit holds every day. Eating at maintenance instead would be 2,759 kcal/day.
Imperial example: 40-year-old man, 5 ft 10 in, 190 lb, sedentary → 1,384 kcal/day
Enter age 40, male, 5 feet 10 inches, 190 lb, sedentary, goal 180 lb, 750 kcal deficit: height converts to 70 × 2.54 = 177.8 cm and weight to 190 × 0.45359237 = 86.2 kg, so BMR = 10 × 86.2 + 6.25 × 177.8 − 5 × 40 + 5 = 1,778, TDEE = 1,778 × 1.2 = 2,134, and the target is 2,134 − 750 = 1,384 kcal/day. The 10 lb (4.5 kg) gap at 750 a day takes about 47 days. Note the target sits above 1,200, so no low-intake warning fires — a smaller person on the same deficit would see one.
How to measure
- Weigh yourself first thing in the morning, after using the bathroom and before eating, in light clothing — and use the same scale each time. A heavy meal or a different scale can swing the reading by a kilogram or more, and the whole calculation keys off that weight.
- Measure height without shoes, standing straight against a wall. Entering 5 feet 10 inches as two numbers (5 + 10), not as a decimal like 5.10 feet, matters: the decimal form understates your height and understates your BMR.
- Pick your activity level honestly, not aspirationally. A desk job with three gym sessions a week is moderately active, not very active — and most people who pick one level too high get a TDEE hundreds of calories above reality, which quietly erases their deficit.
- Re-enter your current weight every few weeks and re-run the tool. As you lose weight your BMR and TDEE fall, so a target that worked at 80 kg is too generous at 75 kg — the goal date only stays honest if the inputs stay current.
- Track intake for a week before trusting the target. Food labels, cooking oils, and drinks are where most people undercount by 200–300 kcal a day, which is most of a 250 deficit on its own.
Assumptions & limitations
Planning estimate
- Estimates only — not medical advice. This tool estimates energy needs from population equations; it does not diagnose, assess risk for any individual, or replace a clinician. Talk to a healthcare professional before starting a deficit, especially below 1,200 kcal/day.
- Mifflin-St Jeor is validated for adults and estimates an average. Your real BMR varies with muscle mass, hormones, sleep, illness, and medication — two people with identical inputs can burn measurably different amounts, and the tool cannot see any of that.
- Activity factors are coarse averages (1.2–1.9). A "moderately active" label covers a wide range of real movement, and the factor is the single biggest error source in the result — an honest activity pick matters more than a precise weight.
- The 7,700 kcal-per-kilogram rule is a useful average, not a law. Real weight loss mixes fat and lean tissue, water shifts hide fat loss for weeks at a time, and metabolic adaptation slows loss as you go — so the goal date is an estimate that drifts, not a schedule.
- The equation is designed for adults. It is not validated the same way for children or teenagers, for pregnant or breastfeeding people, or for people with conditions that change metabolism — the tool does not adjust for any of these, and the low-intake warning is not a substitute for professional guidance.
Frequently asked questions
BMR is what you burn at complete rest — breathing, circulation, body temperature — measured as if you lay in bed all day. TDEE is BMR multiplied by your activity factor, so it includes walking, working, and exercise: it is the intake that holds your weight steady. The brief example makes it concrete: BMR 1,780 at rest, TDEE 2,759 at moderately active — the 979 kcal gap is everything you do in a day.
About 0.45 kg a week, by the 7,700 kcal-per-kilogram rule: 500 × 7 = 3,500 kcal a week, divided by 7,700 = 0.45 kg. In imperial terms that is the classic "pound a week" (3,500 kcal ≈ 1 lb of fat). A 250 deficit gives about 0.23 kg a week and a 750 deficit about 0.68 kg — slower deficits are easier to sustain, which is why the tool offers all three rather than pushing the largest.
For most adults, 250–500 kcal a day is the sustainable range, and the tool warns whenever the resulting target falls below 1,200 kcal/day — a level where meeting nutrient needs from food alone gets difficult. A 750 deficit can be fine for larger people with higher TDEEs, but the smaller your TDEE, the sooner a big deficit pushes you under 1,200. Anyone with a medical condition, a history of disordered eating, or a target under 1,200 should talk to a healthcare professional first.
Because the 7,700 rule assumes every kilogram lost is fat and your burn stays constant — neither is true. Early loss includes water, later loss slows as your BMR and TDEE fall with your weight, and a single week off-plan moves the date. The honest use is to re-enter your current weight every few weeks: each re-run gives a fresh date from where you actually are, and the drift between dates tells you how the plan is really going.
TDEE minus your deficit — never BMR on its own as a target, unless a clinician tells you otherwise. BMR is the at-rest floor; eating at BMR while active is already a large deficit, and for most people it lands under 1,200 kcal/day. The tool’s headline number is always TDEE minus deficit, with BMR shown so you can see the floor it is built on.