A calorie is a unit of energy. Your body spends energy all day: most of it just keeping you alive (breathing, a beating heart, a warm body), some of it digesting food, and the rest on movement. The total is what people mean by "the calories you need". Eat about that much and your weight tends to stay steady.
No two bodies spend the same amount. Size, age, muscle and how much you move all change the number. Try the estimate below. It is a starting point to learn from, not a target to hit exactly.
Your calorie need is a range, not a number. Use the estimate as a starting point, then watch how your weight and energy behave over a few weeks.
The calculator works in two steps. First it estimates your resting energy: what your body burns lying still all day. The Mifflin-St Jeor equation does this from weight, height, age and the sex-specific constant. It is one of the most widely used equations, and it has held up well in comparisons with older equations. It is still an average, and it can be off for an individual by a few hundred kcal either way.
Second, it multiplies by an activity factor (scientists call it the physical activity level, or PAL). A mostly seated day sits around 1.4. A moderately active lifestyle, which EFSA uses as its reference, is about 1.6. Very active people reach 1.8 to 2.0 and above. The bands are broad, and people often rate themselves as more active than they are, so if you are between two choices, the lower one is the safer guess.
Public guidance gives rough averages, such as about 2,000 kcal a day for women and 2,500 for men in the UK NHS guide. EFSA's reference needs for moderately active adults in their thirties run from about 2,000 to 2,600 kcal. Your result probably lands near those, and the difference from them is normal.
The estimate is not a prescription. A practical way to use it: eat in a way that feels satisfying for two to three weeks, keep an eye on your weight trend (not a single weigh-in), and notice your hunger, sleep and energy. If your weight is steady, your real maintenance is close to what you eat. If it drifts, nudge your portions a little rather than starting from a new formula.
Some points worth knowing:
Ask a doctor or dietitian before changing how you eat if you have a medical condition, are pregnant or breastfeeding, have or had an eating disorder, take medication (especially for diabetes or blood pressure), or are under 18 or over 80. If the estimate lands under about 1,200 kcal (women) or 1,500 kcal (men), this page shows that floor instead and suggests you speak to a professional. Nothing here is medical advice.