Fat loss needs a calorie deficit — eating less than you burn. This guide shows how to size yours safely; the live tool gives your exact daily number.
Use our TDEE calculator on the homepage. TDEE = BMR × activity. That is calories to maintain weight.
Learn how to protect muscle: deficit without muscle loss.
Log weekly weight in the Progress Tracker. If loss stalls 2+ weeks, drop another 100–150 kcal or add steps. Recalculate TDEE as you get lighter.
The calculator has two loss goals: Mild loss (250 kcal per day below TDEE) and Loss (500 kcal per day below TDEE). Its weekly estimates use the classic rule that about 3,500 kcal equals 1 lb (0.45 kg) of body weight.
| Daily deficit | Weekly deficit | Estimated change per week |
|---|---|---|
| 250 kcal (Mild loss) | 1,750 kcal | About 0.5 lb (0.23 kg) |
| 500 kcal (Loss) | 3,500 kcal | About 1 lb (0.45 kg) |
| 750 kcal (not a preset) | 5,250 kcal | About 1.5 lb (0.68 kg) |
This rule is only a rough starting point. It assumes that your energy needs stay the same, but they go down as you lose weight, so loss slows over time. Hall and colleagues (2011) showed that the rule overestimates long-term weight loss. Their rule of thumb for an average adult who is overweight: each lasting cut of 10 kcal per day leads to about 1 lb of loss in the end, with about half of it in the first year. The calculator's 12-week projection uses the simple rule, so real results can differ.
A 45-year-old woman is 158 cm tall, weighs 70 kg and has a desk job with little exercise (Sedentary). Her BMR is 1,302 kcal (Mifflin-St Jeor) and her TDEE is 1,302 × 1.2 = 1,562 kcal per day. The table also shows her targets at the Light level (× 1.375).
| Goal | Sedentary (TDEE 1,562 kcal) | Light activity (TDEE 1,790 kcal) |
|---|---|---|
| Maintain | 1,562 kcal | 1,790 kcal |
| Mild loss (−250) | 1,312 kcal | 1,540 kcal |
| Loss (−500) | 1,062 kcal, warning shown | 1,290 kcal |
Her sedentary Loss target is below 1,200 kcal, so the calculator shows a warning (it warns below 1,200 kcal for women and 1,500 kcal for men). Mild loss, or more daily movement at the Light level, would suit her better.
Many experts suggest losing about 0.5–1% of your body weight per week to protect muscle. For a 70 kg person, that is 0.35–0.7 kg per week. Slower loss is also fine. Very large deficits often cause problems:
Do not eat below about 1,200 kcal (women) or 1,500 kcal (men) per day without medical supervision. If you are pregnant, breastfeeding, under 18, or have a medical condition such as diabetes, talk to a doctor or registered dietitian before you start a deficit.
These habits help you lose mostly fat, not muscle:
Your TDEE goes down as your weight goes down, so the same target gives slower results later. Enter your new weight every 4–6 weeks, or after you lose about 5% of your body weight. For example, if the woman above goes from 70 kg to 65 kg, her sedentary TDEE falls from 1,562 to 1,502 kcal.
Some people also plan diet breaks: one or two weeks at maintenance between periods of dieting. In one study of men with obesity, repeating two weeks of dieting and two weeks at maintenance led to more fat loss than dieting without breaks, for the same number of dieting weeks. Breaks are optional.
A calorie deficit means eating fewer calories than you burn (TDEE). Your body uses stored energy (mostly fat) to make up the gap.
A 500 kcal daily deficit targets about 1 lb fat loss per week. Milder 250 kcal deficits are easier to sustain. Avoid going below safe minimums without medical advice.
Enter age, sex, weight, height, and activity to get TDEE, then pick a goal (mild loss, loss, maintain, gain). Eat the target calories consistently and recalculate every 4–6 weeks.
Early weight loss includes water and stored carbohydrate (glycogen), not only fat. After the first one or two weeks, the rate usually slows down. Judge your progress by the trend over several weeks.
Common reasons are eating more than you track, moving less, water retention, or a lower TDEE after weight loss. If the trend stays flat for two weeks of careful tracking, eat 100–150 kcal less per day or walk more.
Yes. Your average over the week matters most. The Weekly cycling planner in the calculator helps you plan higher and lower days around your daily target.
No. A deficit is not suitable during pregnancy or breastfeeding, or for people with a history of eating disorders. Children and teenagers should only diet with medical advice. If you have a health condition or take medicine, ask a doctor or registered dietitian before you start.
Studies and guidelines this page is based on: