Calorie Deficit Calculator
How many calories a day to eat to lose weight, and how long it takes.
Good to know. Half a kilo a week is a deficit of 550 kcal a day: about one large pizza slice fewer and a brisk walk.
Not medical advice. A general estimate for healthy adults.
How it works
In plain words
Your maintenance calories are your resting energy use (Mifflin-St Jeor) times an activity factor. Losing a kilogram of body weight takes a deficit of roughly 7,700 kcal, so a pace of 0.5 kg a week needs about 550 kcal a day less than maintenance.
The formula
resting = 10 × kg + 6.25 × cm − 5 × age (+5 men, −161 women) maintenance = resting × activity deficit per day = kg per week × 7,700 ÷ 7 eat = maintenance − deficit
Worked example
A 35-year-old woman, 70 kg and 165 cm with light exercise, maintains on about 1,918 kcal a day. Losing 0.5 kg a week means 550 kcal less: about 1,368 kcal a day, reaching 65 kg in 10 weeks.
Sources
- Mifflin, St Jeor et al., A new predictive equation for resting energy expenditure in healthy individuals, American Journal of Clinical Nutrition, 1990 Resting energy use.
- Hall, What is the required energy deficit per unit weight loss?, International Journal of Obesity, 2008 Why the 7,700 kcal per kilogram rule is an approximation.
Sources checked September 30, 2026. 4 automated tests check its answers on every change.
About the calorie deficit calculator
To lose weight, you need to take in less energy than you use: a calorie deficit. This calculator estimates how much you use now (your maintenance calories), takes off a deficit that matches the pace you choose, and tells you when you would reach your goal at that pace.
Maintenance calories are your resting energy use, from the Mifflin-St Jeor equation, multiplied by an activity factor. Be honest about activity: most people overestimate it, and a desk job with three gym visits a week is “light”, not “moderate”. A kilogram of body weight lost corresponds to roughly 7,700 kcal (about 3,500 kcal per pound), so 0.5 kg a week needs a deficit of about 550 kcal a day.
A steady 0.25 to 0.5 kg (half to one pound) a week is easier to keep up and preserves more muscle than crash dieting. Faster loss is possible, especially at a higher starting weight, but very low intakes make it hard to get enough protein, vitamins and minerals. As a rule of thumb, women shouldn’t go below 1,200 kcal a day and men below 1,500 without medical supervision.
The goal date is an estimate. As you lose weight, your maintenance calories fall, so progress slows unless you recalculate every few kilos. Water weight also makes the scale jump from day to day: look at the trend over weeks. If you have a health condition, are pregnant or take medication, talk to a doctor before changing how you eat.
Questions people ask
How many calories should I eat to lose weight?
About 550 kcal a day below your maintenance calories to lose 0.5 kg (1 lb) a week. For a moderately active woman that is often around 1,400 to 1,600 kcal.
How big should a calorie deficit be?
250 to 550 kcal a day, for 0.25 to 0.5 kg a week, is a sustainable range for most people.
Why is my weight loss slower than the calculator says?
Your maintenance calories fall as you lose weight, and water weight hides fat loss for a while. Recalculate every few kilos.