Calorie Intake Calculator
How many calories should you eat in a day? This calorie intake calculator gives the working answer in one multiplication: your weight in kilograms times a factor for how active you are. Enter your weight, pick the activity line that honestly describes your week as it is rather than as planned, and it returns your daily calories to maintain your weight, to lose it gently or steadily, and to gain.
One Multiplication, Honestly Labelled
The full science of energy needs — basal metabolic rate from the Mifflin-St Jeor equation, multiplied by an activity factor — collapses, for a typical adult, into a surprisingly stable ratio between body weight and total daily expenditure. That ratio is what this page prices: about 33 kcal per kilogram per day for a moderately active adult, lower for sedentary lives (29), higher for athletic ones (39). The imperial ancestor of the rule is older and famous in gym folklore: 15 kcal per pound to maintain — the same number wearing different units, since a kilogram is 2.2 pounds and 15 x 2.2 = 33. The method's honesty is in its label: it is an estimate built from population averages, trading the full formula's inputs (age, height, sex) for a single measurement nobody has to look up. What it loses in precision it returns in use — a figure you can compute on a napkin, defend in a conversation, and correct with a scale.
Worked Example: 80 Kilograms at the Moderate Line
The defaults: 80 kg at the moderate factor gives maintenance of 2,640 kcal/day — a gentle loss at 2,390, a standard loss at 2,140, and a lean gain at 2,940. Cross-check by the pound rule: 80 kg is 176.4 lb, and 176.4 x 15 = 2,646 kcal — the same answer to within a rounding error, which is the two unit systems agreeing that the underlying ratio is real. Cross-check against the full equation (this hub's maintenance page, Mifflin-St Jeor at the moderate multiplier, for a 30-year-old man of 180 cm): 2,759 kcal — about 4 percent above the simple figure, well inside the method's stated error band, and a fair picture of the trade: the equation spends three extra inputs to buy those 119 calories of refinement. For planning a first month of eating, either number works; the scale's verdict after a fortnight outranks both.
The Factors, Band by Band
Each factor is a life's shape compressed: 29 is the desk and the sofa — under 5,000 steps a day and no deliberate exercise; 31 adds one to three weekly sessions or a walking-rich commute; 33, the default, is three to five training days or a job that keeps its holder moving; 36 is hard training most days; 39 is the rare double shift of physical labour plus sport. The spacing matters more than the labels: each band is worth 2-3 kcal per kilo, which at 80 kg is 160-240 kcal a day — the size of a snack, and the size of the error made by choosing the band you aspire to rather than the band you inhabit. Choose by the week's evidence (a step count is the cheapest witness), and remember the factors assume an average body composition: the very lean burn a little more per kilo, the very overweight a little less, because fat tissue is metabolically quieter than the average the ratio was built on.
Where the Simple Method Wins, and Where It Hands Over
It wins at the start of everything: the first estimate for a new trainee, the sanity check on a diet plan's claims, the quick answer for a body weight the full equations were never validated on. It hands over in three known territories. Age: the per-kilo ratio drifts down across adulthood as lean mass falls, so a 65-year-old's truth sits nearer the bottom of their band. Extremes of composition: competitive bodybuilders and severe obesity both break the average-body assumption in opposite directions. And precision work — clinical nutrition, elite sport, medication-sensitive conditions — belongs to measured metabolism and professional judgement, not to any calculator. The hub keeps both instruments (this quick ratio, and the full Mifflin-St Jeor maintenance page) because they audit each other: when the two disagree wildly, the inputs to one of them are lying, and finding out which is the genuinely useful exercise.
From a Daily Number to a Week of Eating
Multiply by seven before you plan: 2,640 a day is 18,480 a week, and the weekly frame forgives what the daily frame cannot — a 3,400-kcal celebration is not a broken diet but a 760-kcal loan repaid by two gentle days at 2,260. Most successful self-managers quietly run weekly budgets with daily guides, because life is scheduled weekly and appetites are not. The calculator's loss and gain lines translate the same way (a minus-500 day is a minus-3,500 week, the textbook half-kilo of fat), and the translation exposes the real unit of progress: not the perfect day, which nobody strings together, but the honest average, which anybody can.
Children, Pregnancy and Other Special Cases
The per-kilo rule is fitted on adults and must not be stretched over populations whose energy economics differ: children burn far more per kilo (growth is expensive, and paediatric needs run 60-90 kcal per kilo in the young), pregnancy adds roughly 340-450 kcal a day in the second and third trimesters to a woman's pre-pregnancy figure, and lactation adds about 500. Older adults slide down within their band as lean mass falls. In each case the calculator's honest service is the adult baseline it states on its face — departures from that baseline belong to the specific guidance of the relevant professionals, and this page's restraint about it is deliberate.
The Two-Week Calibration, in Practice
Run the fortnight like an experiment, not a judgement: eat at the maintenance figure, weigh on waking three or four mornings a week, and average each week separately. A flat pair of averages crowns the estimate; a drift of a quarter-kilo between the weeks converts, at roughly 250 kcal a day per quarter-kilo per week, into the correction your personal factor needs. Two weeks of data outrank every equation on this hub — including this page's, which says so in its own widget note.
Related Tools
More from the Health Calculators hub: the Maintenance Calorie Calculator — the full Mifflin-St Jeor treatment this page abbreviates — the Carb Calculator for apportioning the total, and the IIFYM Calculator for the complete macro split.
Frequently Asked Questions
How accurate is the weight-times-factor method?
Within roughly 10 to 15 percent for typical adults — call it plus or minus 250-350 kcal at the worked example's size. That band is honest physiology, not sloppiness: measured metabolic rates between two people of identical stats genuinely differ by that much, which is why every method on this hub, simple or full, ends with the same instruction to calibrate against a fortnight of weight trend. The simple method's virtue is reaching its (slightly wider) band with one input instead of four.
Is the rule different for women?
A little, on average: at equal weight and activity, women's maintenance tends to run 1-2 kcal per kilo lower, reflecting average body-composition differences (a higher essential-fat share, which is metabolically quiet tissue). The practical reading: women choosing between two bands should take the lower one as their starting estimate and let the calibration fortnight arbitrate. The full Mifflin-St Jeor page prices the difference exactly (its 166-kcal constant gap); this page folds it into band choice.
What about the 2,000-calorie figure on food labels?
That is a labelling convention — a round reference number chosen so percentages of daily values can be printed — not a recommendation and not your requirement. The defaults above show a moderately active 80-kg adult needing a third more than the label's fiction; a small sedentary adult may need a quarter less. Printing one number for a species whose needs range from 1,400 to 5,000 kcal is a regulatory convenience, and treating it as guidance is the commonest calorie error of all.
When should I recalculate?
Whenever the inputs move: every 5 kg of weight change reprices maintenance by roughly 150-165 kcal at the moderate factor, and a change of job, season or training load can move the band itself. During an active cut or gain, a monthly re-run keeps the targets honest against the new body that is doing the eating — yesterday's deficit becomes today's maintenance with weight loss's full cooperation, which is physiology's sense of humour and the plateau's whole explanation.
Why do two calculators give me different numbers?
Because they are answering with different evidence: this page uses your weight and activity alone, the full equation adds age, height and sex, and a wearable adds its (often generous) guess at your movement. Spreads of 100-300 kcal between methods are normal and are not a contradiction to resolve but an error bar to respect. The resolution procedure never changes: pick the figure whose method you understand, eat at it for a fortnight, and let the weight trend cast the deciding vote — after which the winning method, for you, is whichever one the scale just crowned.
Do these calories include exercise I add later?
The factor already contains the activity you declared — adding workout calories on top double-counts them, the classic tracker error that manufactures phantom budget. If your training load changes durably, change the band; if it was a one-off heroic Sunday, let the weekly average absorb it. The calculator prices the life pattern, not the day, and consistency between the declaration and the eating is the entire method.