How the calculator works
It uses the Mifflin-St Jeor equation to estimate your basal metabolic rate (BMR), the energy your body uses at rest:
- Men: 10 x weight (kg) + 6.25 x height (cm) - 5 x age + 5
- Women: 10 x weight (kg) + 6.25 x height (cm) - 5 x age - 161
BMR is then multiplied by an activity factor (1.2 for a desk-bound day up to 1.9 for very hard training) to estimate your total daily needs. As a rough comparison, the NHS uses 2,500 kcal a day for an average man and 2,000 for an average woman.
Using the number sensibly
- Treat the result as a starting estimate. Real needs can differ by a few hundred calories either way.
- A deficit of about 500 kcal a day usually gives a loss of around 0.5 kg (1 lb) a week. Faster isn't better: very low intakes cost muscle and are hard to keep up.
- Check your weight trend over two to three weeks, then adjust by 100 to 200 kcal if nothing changes.
- Protein, fibre and sleep make a deficit much easier to stick to. See omelette vs boiled egg for weight loss for a simple example.
Thinking about weight-loss medicines? Read Wegovy pill vs weekly injections. To check where your weight sits now, use the BMI calculator.
Who shouldn't rely on this calculator
- Anyone under 18, or pregnant or breastfeeding: your needs are different.
- People with diabetes on insulin or sulfonylureas: changing intake can cause low blood sugar, so plan it with your doctor.
- Anyone with a current or past eating disorder. Please speak to a professional you trust before counting calories.
- People with kidney, liver or heart disease, who may need a tailored diet.
Frequently asked questions
What's the difference between BMR and maintenance calories?
BMR is what you'd burn lying still all day. Maintenance calories add your daily movement and exercise on top.
How many calories should I eat to lose weight?
For most adults, about 500 kcal below maintenance, without dropping under roughly 1,200 kcal (women) or 1,500 kcal (men) unless a clinician is supervising.
Why am I not losing weight on my target?
The usual reasons are underestimated portions, drinks and snacks that don't get counted, and an activity level set too high. Water retention can also hide fat loss for a week or two.
These tools give general estimates for adults and are not a diagnosis or a substitute for advice from a doctor. If you have symptoms or a health condition, please consult a qualified healthcare professional.