Calorie Deficit and Surplus Calculator
Turns a daily deficit or surplus into a calorie target and an expected weekly change. Not suitable in pregnancy or for under-18s.
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The formula
target = maintenance − deficit (never below the floor) target = maintenance + surplus weekly change = daily change × 7 ÷ 7,700
Maintenance comes from the Mifflin-St Jeor equation and your activity. The floor is 1,200 kcal a day for women and 1,500 for men.
What to watch out for
Maintenance uses the Mifflin-St Jeor equation (1990). The floors of 1,200 and 1,500 kcal are the lower end of the intakes in the 2013 AHA/ACC/TOS obesity guideline (Jensen and colleagues). The NHS suggests losing about 0.5–1 kg a week. Hall and colleagues (Lancet, 2011) modelled how energy use adapts as weight changes, which is why a fixed kcal-per-kg rule tends to overstate long-term loss.
Frequently Asked Questions
How big should a calorie deficit be?
Around 500 kcal a day is a common starting point. For a 35-year-old woman, 168 cm and 80 kg, with light activity, that gives 1,582 kcal a day and about 0.45 kg a week.
What happens if I ask for a very large deficit?
The target stops at the floor. For the same woman, a 1,500 kcal deficit still shows 1,200 kcal a day, which is a real deficit of 882 kcal.
How big a surplus should I use for bulking?
Often 200–300 kcal a day. A surplus of 250 kcal comes to about 0.23 kg a week. How much of that is muscle depends on your training.