How the calorie calculator works
The calculator first estimates your basal metabolic rate (BMR): the calories your body burns at complete rest just to keep you alive. It uses the Mifflin-St Jeor equation, which research has found to be one of the more accurate formulas for most adults:
Women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161
Men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
It then multiplies your BMR by an activity factor to estimate your total daily energy expenditure, often called your maintenance calories. Eat about that much and your weight should stay roughly the same.
| Activity level | What it means | Multiply BMR by |
|---|---|---|
| Sedentary | Desk job, little exercise | 1.2 |
| Lightly active | Light exercise 1 to 3 days a week | 1.375 |
| Moderately active | Exercise 3 to 5 days a week | 1.55 |
| Very active | Hard exercise 6 to 7 days a week | 1.725 |
| Extremely active | Physical job plus training | 1.9 |
Most people overestimate how active they are. If you walk the dog and do a couple of gym sessions a week but sit at a desk all day, "lightly active" is probably closer.
How many calories do I need a day?
The NHS says an average man needs around 2,500kcal a day and an average woman around 2,000kcal a day to maintain a healthy weight. The 2,000kcal figure is also the reference intake (RI) printed on UK food labels. Your own needs could be quite different depending on your age, size and how much you move, which is what this calculator estimates.
Worked example
A 35-year-old woman who is 165cm tall, weighs 70kg and exercises three to five times a week:
- BMR: (10 × 70) + (6.25 × 165) − (5 × 35) − 161 = 700 + 1,031.25 − 175 − 161 = 1,395kcal
- Maintenance: 1,395.25 × 1.55 = 2,163kcal a day
- To lose about 0.5kg a week: 2,163 − 500 = 1,663kcal a day
A 40-year-old man who is 180cm and 86kg with a lightly active lifestyle has a BMR of 1,790kcal and maintenance calories of 2,461kcal. Cutting 500kcal gives a target of 1,961kcal.
Losing weight safely
To lose weight you need to take in fewer calories than you use. The NHS recommends aiming to lose 0.5kg to 1kg (1 to 2lb) a week, and its 12-week weight loss plan suggests no more than about 1,900kcal a day for most men and 1,400kcal for most women while losing weight. This calculator deliberately keeps things gentle:
- The biggest cut it offers is 600kcal a day.
- It won't suggest fewer than 1,200kcal a day for women or 1,500kcal for men. Very low calorie diets (under 800 to 1,200kcal) are only suitable for some people, with support from a GP or dietitian.
- As you lose weight your maintenance calories fall, so recalculate every few kilos.
Small, lasting changes tend to work better than crash diets: swapping sugary drinks for water, smaller portions, more vegetables and fibre, and moving more. Alcohol can add a surprising number of calories; check your weekly total with our alcohol units calculator.
Speak to your GP before changing your diet if you have diabetes or another health condition, take regular medication, are pregnant or breastfeeding, or have a history of eating problems. This calculator is for adults; children and teenagers have different needs.
Is this calculator accurate?
Any formula is an estimate. Two people of the same age, height and weight can burn quite different amounts depending on muscle mass, genetics and how much they fidget. Treat the result as a starting point: eat that amount for two or three weeks, weigh yourself at the same time each week, and adjust up or down by 100 to 200kcal if your weight is moving in the wrong direction. Not sure if your weight is in the healthy range? Check your BMI first.
Frequently asked questions
How many calories should a woman eat a day?
The NHS says an average woman needs around 2,000kcal a day to maintain her weight. A 35-year-old woman of 165cm and 70kg who exercises a few times a week needs about 2,160kcal, while a smaller or less active woman may need under 1,800kcal.
How many calories should a man eat a day?
Around 2,500kcal a day for an average man, according to the NHS. Taller, heavier or very active men need more, and older or less active men need less.
How many calories should I cut to lose weight?
A deficit of 500 to 600kcal a day below your maintenance calories is a common, sensible target for steady weight loss. The NHS suggests aiming to lose 0.5kg to 1kg a week.
What is BMR?
Basal metabolic rate is the number of calories your body uses at rest to breathe, circulate blood and keep your organs working. For most people it's the biggest part of the calories they burn each day.
Is 1,200 calories a day too low?
For many adults 1,200kcal is below what they need to stay healthy, especially men or anyone active. Don't go below it without speaking to your GP or a dietitian.
Last reviewed October 2026 using 2026/27 figures. This calculator gives an estimate for guidance only.