The short answer
Most adult women hold their weight somewhere between about 1,600 and 2,400 kcal a day, most adult men somewhere between 2,000 and 3,000. That is a wide span, because "adult" covers a five-foot office worker and a six-foot-four labourer with the same word. The calculator above narrows it down to one number, built from your sex, age, height, weight and how much you move, then adjusted for what you want your weight to do next. Fill in the six fields, choose lose, stay the same or gain, and read your answer off the panel.
Why the honest answer is "it depends"
Ask five people how many calories they should eat and a good answer sounds different five times, because the number rides on three things: how big you are, how much you move, and what you want your weight to do next.
Size comes first. A taller or heavier body spends more energy just existing, more tissue to keep warm, a bigger frame to carry, so two adults of the same age and activity level can need totals several hundred kcal apart without doing anything differently.
Movement comes second, and it swings the total harder than most people expect. It rarely means the gym alone: someone on their feet all day, walking a delivery round or standing at a till, spends more by six o'clock than a desk-bound colleague could match with a single evening run. The activity dropdown is a rough attempt at capturing that whole day, not just the planned exercise inside it.
Goal comes third, and it is the only lever you actually choose. Size and movement describe the person you already are; goal is the adjustment you make on purpose, pulling the number down to lose weight or pushing it up to gain.
What 500 fewer, or 300 more, calories looks like on a plate
A number on a screen does not mean much until it lands on a plate. Five hundred calories, this calculator's cut for losing weight, is roughly a shop meal-deal sandwich and a bag of crisps, or two glasses of wine, or a large flapjack with a milky coffee. Miss that much most days and the arithmetic says you should lose somewhere around half a kilogram, a little over a pound, a week.
Three hundred calories, the gain side, is smaller than it sounds: a large banana with a spoonful of peanut butter, or an extra chicken thigh and a scoop of rice at dinner. Added to a day that already holds your weight steady, that nudges the scale up gently, roughly a quarter of a kilogram a week, without much extra food at any single meal.
Neither change needs a kitchen scale glued to your hand or a special shopping list. Losing the sandwich-and-crisps equivalent, or adding the banana-and-peanut-butter one, on most days is the whole mechanism. Getting the starting number right is what makes that swap actually work.
When to use a more detailed tool
This page is built to answer the question in one visit: enter a handful of details, read the number, get on with your day. That simplicity is deliberate, and it leaves out finer controls kept on two other pages for anyone who wants them.
The Daily Calorie Calculator shows the same maintenance figure worked out three ways side by side, adds a macro split, and compares every activity level at once instead of picking one from a list. The Calorie Deficit Calculator is worth a visit once losing weight becomes an actual plan: name a goal weight and it hands back a finish date, a week-by-week chart, and a deficit sized to a safe pace rather than a flat 500 kcal cut.
Neither tool disagrees with this one. Both use the same Mifflin-St Jeor formula underneath and land close to the same number for the same details; they simply show more of the working.
Questions people ask
Is 1,500 kcal enough for a woman?
For a lot of adult women, yes: 1,500 kcal sits above the 1,200 kcal everyday floor this calculator uses, so it is a workable weight-loss number rather than a starvation one. Whether it suits you depends on your size and activity; a taller or more active woman might find it a steep cut, a smaller or older woman might find it close to maintenance already. Constant hunger at that number means eat a little more and lose a little slower.
Do I need to eat back the calories I burn exercising?
Generally no. The activity level chosen on the form already has a training allowance built into it, so the number above assumes you are moving. Adding food back because a watch reported a 400 kcal workout usually double-counts calories the formula had already set aside, and wrist trackers tend to overestimate exercise burn.
Why do other calculators give me a different number?
Small differences in formula, activity multiplier or how a deficit is sized routinely move the answer by 100 to 300 kcal without either page being wrong. This one uses Mifflin-St Jeor, the strongest performer in modern validation studies; older formulas such as Harris-Benedict are still common online and read a little higher. Treat any single number, this one included, as a starting point and let a few weeks of real weigh-ins settle the argument.
Should teenagers use this calculator?
No, adults only. This tool is built around formulas validated for stable adult weight; growing teenagers have higher energy needs those formulas were not designed to capture, and cutting calories during those years can interfere with growth. Anyone under 18 should speak to a GP, school nurse or registered dietitian instead.
How fast will I actually lose or gain weight at this number?
A steady 500 kcal deficit works out to roughly half a kilogram, a little over a pound, most weeks; a 300 kcal surplus works out to a slower quarter of a kilogram or so. Both are averages over several weeks, not a promise for any single one. Water, salt and how much food is still moving through your gut can shift the scale by a kilogram overnight with no fat involved.
This calculator estimates energy needs for healthy adults and is not medical advice. Speak to a GP or registered dietitian before changing your calorie intake if you are pregnant or breastfeeding, under 18, recovering from disordered eating, or managing a medical condition such as diabetes or a thyroid disorder.