Calorie deficit calculator
Estimate how many calories a day keep your weight steady, and how many to eat to lose weight at a steady pace.
An estimate: real needs vary by about 10% either way. Adjust after 2 to 3 weeks based on how your weight actually changes.
Not for pregnancy, breastfeeding, under-18s, or anyone with, or recovering from, an eating disorder. Talk to a doctor or dietitian.
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How this is worked out
- Your resting energy (BMR) uses the Mifflin–St Jeor equation: 10 × weight in kg + 6.25 × height in cm − 5 × age, then + 5 for men or − 161 for women. If you choose "prefer not to say", the calculator uses the average of the two.
- Your maintenance calories are your BMR times an activity factor: 1.2, 1.375, 1.55, 1.725 or 1.9, from mostly sitting to extremely active.
- The daily deficit uses the common rule of thumb that about 7,700 calories equal 1 kg of body fat (3,500 per pound). For 0.5 kg a week, that is 7,700 × 0.5 ÷ 7 = 550 calories a day.
- Your target is maintenance minus the deficit, rounded to the nearest 10. It never goes below 1,200 (women, or not said) or 1,500 (men).
Source: Mifflin MD, St Jeor ST and others, "A new predictive equation for resting energy expenditure in healthy individuals", American Journal of Clinical Nutrition, 1990. It is the equation dietitians most often use for adults.
What this doesn't account for
- Your body composition. Very muscular people usually need more than the equation predicts.
- Your body adjusting. As you lose weight, you need fewer calories, so progress slows. Recalculate every few kilos.
- Medical conditions and medicines, such as thyroid problems, that change how much energy you use.
- Pregnancy, breastfeeding, under-18s and eating disorders. This calculator is not for those situations: talk to a doctor or dietitian.
- The goal date. It is a straight-line estimate; real weight loss goes up and down from week to week.
Common questions
How many calories should I eat to lose weight?
A common starting point is your maintenance calories minus 300 to 500 a day, which is roughly 0.25 to 0.5 kg (0.5 to 1 lb) a week. Use the calculator above for your own estimate, then adjust it based on how your weight actually changes.
Is a 500 calorie deficit enough?
For many adults, eating 500 calories a day below maintenance leads to about 0.5 kg (around 1 lb) a week at first. Progress usually slows as your weight falls, because a smaller body needs less energy.
What is the lowest number of calories I should eat?
General guidance is not to go below about 1,200 calories a day for women or 1,500 for men without medical supervision. Very low intakes make it hard to get enough protein, vitamins and minerals.
Why has my weight stopped going down?
Changes in water and food in your gut can hide fat loss for a week or two. If nothing has changed after 2 to 3 weeks, your maintenance may be lower than estimated: recalculate with your new weight, or eat about 100 to 200 calories a day less.
Does exercise change my calorie target?
Yes. Your activity level sets your maintenance calories. Choose the level that matches a typical week, not your best week.
Can I use this during pregnancy or breastfeeding?
No. This calculator is not for pregnancy or breastfeeding. Talk to your midwife, doctor or a dietitian about what to eat.