Calorie calculator: your estimated daily needs

What basal metabolic rate and daily energy expenditure actually measure

Two numbers sit behind every estimate on this page. The first is your basal metabolic rate (BMR): the energy your body would use over 24 hours if you did nothing but lie still, since it only covers what keeps your organs, brain and cells running. The second is your total daily energy expenditure (TDEE), which adds the energy spent on everything else — walking, working, digesting food, exercising — on top of that baseline. TDEE is always the larger of the two figures, because it is built from BMR plus whatever activity you add to a day.

Neither number is something a calculator can measure directly. Both are estimated from an equation built on population averages, using your height, weight, age and sex as inputs. That is worth remembering every time you read a result: it describes what people who share your measurements tend to need, similar in spirit to how our ideal weight guide works from formulas rather than from a measurement taken on you specifically.

The Mifflin-St Jeor equation, worked through with real numbers

This calculator estimates basal metabolic rate with the Mifflin-St Jeor equation, one of the most widely used formulas for this purpose. It uses a different constant for each sex, because average body composition differs between men and women at the same height and weight:

• Men: (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5
• Women: (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161

Take a 35-year-old woman who is 165 cm tall and weighs 65 kg, with a sedentary lifestyle. Her basal metabolic rate works out to (10 × 65) + (6.25 × 165) − (5 × 35) − 161, which is 650 + 1,031.25 − 175 − 161 = 1,345.25 kcal a day — shown on this calculator rounded to the nearest ten, 1,350 kcal/day, since a finer figure would suggest a precision the formula does not have. Applying the sedentary activity factor of 1.2 gives her estimated total daily energy expenditure: 1,345.25 × 1.2 = 1,614.3 kcal a day, rounded to 1,610 kcal/day. That single number, her maintenance level, is the anchor every target on this page is built from.

Activity levels are self-reported benchmarks, not measurements

The activity level you choose multiplies your basal metabolic rate by a fixed factor, from 1.2 for a sedentary routine up to 1.9 for a very demanding one. These factors are conventions built around how people describe their week, not readings from a sensor attached to a body. Two people who both describe themselves as “moderately active” can move through very different weeks and still land in the same bracket. Picking a level is an honest approximation, not a precise input: when unsure, choosing the lower of two plausible levels avoids overstating what a day actually burns.

Why this calculator never drops below your basal metabolic rate

A number such as “1,200 calories a day” circulates widely as a supposed universal floor for weight loss. It is repeated often enough to look like an established rule, but it is not tied to any verifiable source, and it could not be, because it treats every body as identical. A basal metabolic rate under 1,200 kcal is entirely plausible for a small, older woman, while a tall, muscular man can have one well above 2,000 kcal — the same fixed number would already be too restrictive for one and meaningless for the other.

This calculator uses a different kind of floor: your own basal metabolic rate, calculated from your own height, weight, age and sex. The weight-loss target normally applies a reduction of 500 kcal a day below your total daily energy expenditure, a widely used starting point for a gradual loss; the weight-gain target adds a smaller 300 kcal a day, since a large surplus mainly adds fat rather than muscle. Whenever that 500 kcal reduction would push the target below your basal metabolic rate, the target is raised back up to that number instead, and a warning explains why. In the example above, the plain reduction would have suggested about 1,110 kcal/day — below her basal metabolic rate of 1,350 kcal/day — so the target shown is raised to 1,350 kcal/day instead.

What this estimate cannot tell you

Body composition

The equation only uses height, weight, age and sex, so it cannot distinguish muscle from fat: two people of the same height, weight and age get exactly the same estimate even if one carries visibly more muscle. Muscle tissue uses more energy at rest than fat tissue does, so a highly muscular person’s true basal metabolic rate typically runs higher than this formula suggests — a blind spot similar to the one described in our page on BMI limitations.

Individual variability

A formula built on population averages describes a middle point, not any one person exactly. Genetics, medical conditions, medication, sleep and hormonal factors can all shift real energy expenditure away from the estimate. That is why the result is best treated as a starting point to adjust from over time, based on how your own weight actually responds, rather than as a fixed and final number.

Metabolic adaptation

Sustained changes in how much you eat can shift how efficiently your body uses energy, a phenomenon usually described as metabolic adaptation. An estimate produced on a single day does not account for how your body might adjust after weeks or months at a new intake level, which is another reason to revisit the numbers periodically rather than treat one calculation as valid indefinitely.

When to talk to a health professional

Speak to a doctor before making a significant change to how much you eat if you are managing a medical condition, taking medication that affects appetite or metabolism, pregnant or breastfeeding, or if your relationship with food or your weight feels difficult to manage on your own. A professional can assess what this calculator cannot: your medical history, your body composition and how your body responds over time. Our page on BMI in adults covers a related but different reference range, useful if you would rather read several indicators together than rely on one number alone.