Calorie calculator

How this calorie calculator works

It uses the Mifflin-St Jeor equation, the formula most dietitians use because it has been the most accurate in comparisons against measured metabolic rate. It first works out your BMR (the calories your body burns just staying alive), then multiplies that by an activity factor to get your TDEE - the calories you burn in a normal day including work and training. Your goal then adds or removes a sensible amount from that number.

The equations, if you want to check them: men 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5; women the same but − 161 instead of + 5.

Picking the right activity level

This is where most people go wrong, and it is usually in the direction of picking too high. A 45-minute gym session three times a week is "light", not "moderate". If you are on site all day carrying materials, "very active" is fair. If in doubt, pick the lower option, run it for two weeks, and let the scales tell you.

What the macros mean

Protein is set at 1.8–2 g per kg of bodyweight, which is the range that protects muscle in a deficit and builds it in a surplus. Fat sits around 0.9 g per kg so hormones and energy stay steady. Carbs fill in the rest. You do not have to hit these to the gram - protein is the one that matters most; the other two can flex day to day.

If the number looks low

If you are a smaller person aiming to lose fat, the target can come out in the 1,300–1,600 range and that feels harsh. Two options: pick the slower fat-loss goal, or - better - add a bit of movement (a daily walk adds 150–300 kcal of burn) so you can eat more while still losing. Fat loss on more food is easier to stick to.

FAQs

How many calories should I eat to lose weight in the UK?

For most adults, 300–500 kcal below your maintenance (TDEE) gives roughly 0.25–0.5 kg of fat loss a week. The calculator above works out your maintenance from your age, sex, height, weight and activity, then takes the deficit off. NHS guidance gives 2,500 kcal a day for men and 2,000 for women as a general average, but your own number can be a long way from that.

Is this calculator accurate?

The formula is accurate to within about 10% for most people. Real-world burn varies with genetics, sleep, how much you fidget and how honest the activity setting is. Treat the result as a starting point and adjust after two weeks of tracking your weight.

Should I eat back calories I burn in the gym?

No - the activity level already includes your training. Adding exercise calories on top is the most common reason people 'in a deficit' don't lose weight.

What is the difference between BMR and TDEE?

BMR is what you burn lying in bed all day. TDEE is BMR plus everything you actually do - walking, work, training, digesting food. You eat according to TDEE, not BMR.