Calorie Needs Calculator
Work out your BMR and total daily energy needs from age, sex, height, weight, and activity level — using the Mifflin-St Jeor equation.
At rest your body burns about 1,699 kcal a day (BMR). Adjusting for your activity level, your total daily energy expenditure is 2,633 kcal — the calories you'd eat to maintain weight.
Daily calories by goal
Results update as you type. The Mifflin-St Jeor equation is the most accurate widely used formula at population level, but individual energy expenditure varies — treat the numbers as a starting estimate, not a prescription.
Formula
The Mifflin-St Jeor BMR equation:
BMR = 10·kg + 6.25·cm − 5·age + s, where
s = +5 for males, s = −161 for females. TDEE is BMR multiplied by
an activity factor (sedentary 1.2 → extra-active 1.9). Goal calories are TDEE shifted by
±500 or ±1000 — the latter giving roughly 1 kg of weight change per week (3,500 kcal ≈ 0.45
kg of fat).
When this calculator helps
Knowing roughly how many calories your body burns in a day is the foundation of any sensible eating plan, whether you want to lose a bit of weight, hold steady, or build up. Use this calculator when you are trying to put a number on your daily energy needs before deciding how much to eat — for example when starting at the gym, planning meals for the week, or working out why the scales have not moved. It gives you a maintenance figure (TDEE) plus targets for losing or gaining, all in kcal, the unit used on UK food labels.
It is built for everyday planning rather than clinical precision. If you have ever wondered whether the NHS '2,000 kcal for women, 2,500 for men' guideline actually fits you — it is only an average, and your real needs depend on your age, height, weight and how active you are — this calculator gives you a personalised estimate instead of a one-size-fits-all number.
How to read your result
Two figures matter. Your BMR (basal metabolic rate) is what you would burn lying in bed all day doing nothing, and it is usually the largest single chunk of your daily total. Your TDEE (total daily energy expenditure) takes that BMR and multiplies it by an activity factor to reflect how much you actually move — TDEE is the number to eat to keep your weight stable.
From maintenance, the goal targets simply add or subtract calories. A deficit of around 500 kcal a day points towards losing roughly half a kilo (about a pound) a week, which is the steady pace the NHS recommends; a surplus does the reverse for gaining. The activity multiplier is where most of the error creeps in, so if your weight is not changing the way the numbers predict, your true activity level is probably a notch lower than you picked.
A worked example
Take a 30-year-old woman, 165 cm tall (about 5 ft 5 in), weighing 68 kg (roughly 10 st 10 lb), who works a desk job and walks a little. Her BMR from the Mifflin-St Jeor formula is about 1,400 kcal. Multiplying by a lightly active factor of around 1.375 gives a TDEE near 1,925 kcal — close to the NHS 2,000 kcal average, which makes sense for someone of average build. To lose about half a kilo a week she would aim for roughly 1,425 kcal a day, sitting just above the 1,200 kcal floor for women.
Common mistakes to avoid
Most disappointment with calorie targets comes from a handful of avoidable errors rather than anything wrong with the maths.
- Overestimating your activity level — most people pick a bucket too high, which inflates TDEE and stalls weight loss.
- Treating the figure as exact; it carries a ±10% margin, so use it as a starting point and adjust by watching the scales over a few weeks.
- Chasing a crash deficit of 1,000 kcal or more, which is hard to sustain and risks dropping below the safe calorie floor.
- Forgetting to recalculate as your weight changes — a lighter body burns fewer calories, so the target drifts over time.
UK guidance and reference points
The figures everyone quotes — around 2,000 kcal a day for women and 2,500 for men — are NHS reference intakes for an average adult, not personal targets, and they assume a moderate activity level. Your own TDEE from this calculator may sit well above or below those numbers depending on your size and how active you are, which is exactly why a personalised estimate is more useful than the headline average.
UK food labels show energy in both kcal and kilojoules, with kcal the figure most people track. If you weigh yourself in stones and pounds, the calculator accepts feet and inches and pounds too, then works in the metric figures the Mifflin-St Jeor formula uses. For weight loss the NHS and the British Dietetic Association both favour a gentle 500 kcal deficit over rapid loss; if you have a medical condition or want supervised support, speak to your GP rather than relying on a calculator alone.
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Frequently asked questions
What's the difference between BMR and TDEE?▾
BMR (basal metabolic rate) is what your body burns at complete rest — keeping organs running, body temperature stable, basic biological processes going. It's roughly 60–75% of total energy expenditure for a sedentary person, less for an active one. TDEE (total daily energy expenditure) is BMR plus everything else: walking, working, exercise, fidgeting, digestion. TDEE is the figure you'd eat to maintain weight.
How accurate is the Mifflin-St Jeor formula?▾
It's the most accurate widely used BMR equation at population level — the American Dietetic Association reviewed several formulas in 2005 and rated Mifflin-St Jeor most accurate for healthy adults. Individual variation is still ±10% or so: two people with identical height/weight/age can have meaningfully different metabolic rates due to body composition (muscle burns more than fat) and genetics. Treat the result as a starting estimate, not a precise prescription.
Why does the calculator need my sex?▾
Because the Mifflin-St Jeor equation has a sex-specific constant (+5 for males, −161 for females) that captures the average difference in body composition. The formula isn't ideal for people whose body composition doesn't match the binary assumption (transgender people on hormone therapy, athletes with very high muscle mass) — in those cases, treat the number as a starting point and adjust based on how your weight responds over a few weeks.
What activity level should I pick?▾
Be honest, and lean conservative. 'Sedentary' fits desk work with no real exercise (most office jobs). 'Lightly active' is 1–3 light gym sessions/week or daily walking. 'Moderately active' is 3–5 proper sessions a week. 'Very active' is 6–7 hard sessions OR a physically demanding job. 'Extra active' is athletes and people doing both daily training AND a physical job. Most people overestimate their activity — start one notch lower than feels right.
Why is the deficit floor 1,200 kcal?▾
Below 1,200 kcal/day for women (~1,500 for men) it becomes hard to hit basic vitamin and mineral targets without supplementation, and metabolism downregulates faster, making the deficit progressively harder to sustain. The NHS recommends slow steady deficits (250–500 kcal/day, half a kilo a week) over rapid loss for most people. Aggressive deficits work briefly but rebound is common — and unsupervised very-low-calorie diets carry medical risks including gallstones, electrolyte disturbance, and muscle loss.
Should I cut by 1,000 kcal/day to lose weight fast?▾
Probably not. A 1,000 kcal/day deficit theoretically gives ~1 kg/week loss but is hard to sustain, often produces fatigue and food preoccupation, and risks the calorie floor. The NHS, BDA, and most evidence-based weight services recommend 500 kcal/day deficits as the default, accepting slower loss in exchange for adherence and preserving lean mass. The numbers in this calculator are mathematical, not endorsements.