A calorie deficit means eating fewer calories than your body burns. The gap is what your body takes from stored fat. This calculator turns a weight goal into a daily number: tell it how fast you want to get there and it tells you how much to eat, or tell it how much you plan to eat and it tells you when you will arrive.
How it is calculated
- Your maintenance calories (TDEE) come from the Mifflin-St Jeor equation for basal metabolic rate, multiplied by your activity level.
- One kilogram of body fat holds roughly 7,700 kcal (about 3,500 kcal per pound).
- Deadline mode: daily deficit = weight to lose × 7,700 ÷ days available. Calories to eat = TDEE − deficit.
- Calories mode: deficit = TDEE − calories you eat. Days needed = weight to lose × 7,700 ÷ deficit.
Example
A lightly active 30-year-old man, 175 cm and 85 kg, burns about 2,470 kcal a day. To reach 75 kg in 12 weeks he needs to lose 10 kg, or 77,000 kcal, over 84 days: a deficit of about 917 kcal a day. He would eat about 1,560 kcal a day. That is close to the upper limit of a safe pace, and the table of options shows that 20 weeks at a 550 kcal deficit is much easier to keep.
What counts as a safe deficit
Most guidelines suggest losing 0.5–1 kg (1–2 lb) a week, which is a deficit of roughly 500–1,000 kcal a day. Going lower than 1,200 kcal a day for women or 1,500 for men makes it hard to get enough protein and micronutrients and is usually only done under medical supervision. A moderate deficit you can hold for months beats an aggressive one you abandon in three weeks.
Why the straight line is only an estimate
The 7,700 kcal rule is a simplification. In the first one or two weeks the scale drops faster because of water and glycogen. Later, a lighter body burns fewer calories, so the same intake produces a smaller deficit. Research models such as the NIH Body Weight Planner show that real loss slows over time. The plan here is a good starting point; recalculate every 4–5 kg and adjust by 100–200 kcal if your weekly average stalls for two weeks.
Frequently asked questions
How many calories should I cut to lose weight?
A deficit of 500 kcal a day leads to about 0.5 kg (1 lb) a week for most people. Enter your target and deadline above to see the exact number for you, and check that it stays above the minimum for your sex.
Is a 1,000 calorie deficit safe?
It is the upper end of what most guidelines allow, giving about 1 kg a week. It is usually only sustainable for people with a lot of weight to lose and enough maintenance calories to stay above 1,200–1,500 kcal a day. Below that, talk to a doctor.
Why am I not losing weight in a calorie deficit?
The usual reasons: portions are larger than logged (most people under-count by 20–30%), activity level is set too high, or water retention hides fat loss for a week or two. Compare weekly averages, not daily weights, and lower intake by 100–200 kcal if the two-week trend is flat.
Should I eat back the calories I burn exercising?
If you picked an activity level that already includes your workouts, no. Eating back exercise calories on top of that counts them twice, which is the most common way a planned deficit disappears.
How long does it take to lose 10 kg?
At a standard 500 kcal deficit, about 20 weeks. At 750 kcal, about 13 weeks. Set your own target above and the week-by-week plan shows the dates.
Sources
- Mifflin MD et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr, 1990
- Hall KD et al. Quantification of the effect of energy imbalance on bodyweight. The Lancet, 2011 — why the 3,500 kcal per pound rule overestimates long-term loss
- NIH Body Weight Planner
- CDC: Losing weight — healthy weight loss
By Calcelate Team. Formula from the sources above.
- 2026-09-13 · Formula and texts checked