The short answer
A calorie deficit means eating fewer calories than your body uses. This calculator finds your maintenance calories, then the daily target needed to reach your goal weight in the time you choose. Targets are never below 1,200 kcal (women) or 1,500 kcal (men), or more than 25% below maintenance. It also estimates your goal date.
Formulas and sources are named on this page. How we calculate.
How this is calculated
The calculator estimates how many calories you burn, works out the weekly loss your goal needs, and converts that into a daily calorie deficit.
Maintenance (TDEE) = Mifflin–St Jeor BMR × activity factor
Weekly loss needed (kg) = (current weight − goal weight) ÷ weeks
Daily deficit (kcal) = weekly loss × 7,700 ÷ 7
Daily target = maintenance − daily deficit, then raised if it breaks a safety limit
Worked example
A 35-year-old man, 180 cm tall, weighing 85 kg, moderately active (factor 1.55), who wants to reach 75 kg in 20 weeks.
- BMR = 10 × 85 + 6.25 × 180 − 5 × 35 + 5 = 1,805 kcal, so maintenance = 1,805 × 1.55 = about 2,800 kcal.
- Weight to lose = 85 − 75 = 10 kg, so the pace is 10 ÷ 20 = 0.5 kg a week.
- Daily deficit = 0.5 × 7,700 ÷ 7 = 550 kcal, so the target is about 2,800 − 550 = 2,250 kcal a day.
- Safety check: 2,250 is above the 1,500 kcal floor and less than 25% below maintenance, so no limit applies.
- Projected weight: about 83 kg at week 4, 81 at week 8, 79 at week 12, 77 at week 16 and 75 kg at week 20.
What happens when the timeframe is too fast
If the time you pick would need a deficit above 25% of maintenance, below the calorie floor, or more than about 1 kg a week, the target is raised to the safe limit. The page then tells you how long the goal will really take at that limit, and gives you that date instead.
Why dates are only a guide
The 7,700 kcal per kilogram figure assumes a steady straight-line loss. Research by Hall and colleagues shows that weight loss slows over time as the body adapts, so real progress is usually slower than the arithmetic. Treat the goal date as a target to review every few weeks, and adjust with a doctor or dietitian if needed.
Weekly weight loss and the daily deficit it needs
Each kilogram of body-weight change is estimated at about 7,700 kcal, so a daily deficit builds up to a weekly loss as follows.
Pace of weight loss and daily calorie deficit| Loss per week | Daily deficit | Comment |
|---|
| 0.25 kg (0.6 lb) | 275 kcal | Gentle and easiest to keep up |
| 0.5 kg (1.1 lb) | 550 kcal | Gentle and easiest to keep up |
| 0.75 kg (1.7 lb) | 825 kcal | Moderate |
| 1 kg (2.2 lb) | 1,100 kcal | Fast, upper limit used here |
Safety limits used by this calculator
Limits on calorie targets| Who | Limit |
|---|
| Women | 1,200 kcal |
| Men | 1,500 kcal |
| Everyone | No more than 25% below maintenance |
| Everyone | No more than about 1 kg (2 lb) lost per week |
Diets of 800 kcal a day or less are classed as very low-calorie diets and need medical supervision. See our calorie calculator for the same limits across every goal.
Frequently asked questions
How big a calorie deficit is safe?
For most healthy adults, a gradual loss of about 0.5 to 1 kg (1 to 2 lb) a week is considered safe and easier to keep up. This calculator never suggests fewer than 1,200 kcal (women) or 1,500 kcal (men), or more than 25% below maintenance. Always speak to a doctor first if you have a medical condition.
Does a 500 calorie deficit really mean 1 pound a week?
It is a rule of thumb: 3,500 kcal is about one pound of body weight, so 500 kcal a day adds up to about a pound a week. In practice weight loss slows as your body adapts, so the loss tends to be smaller than the arithmetic over a long period.
Why is my daily target higher than the pace I chose?
The target was raised to keep to a safety limit: the calorie floor, a deficit of no more than 25% of maintenance, or a loss of no more than about 1 kg a week. The page shows the pace you would really get and the longer time it takes.
How accurate is the goal date?
It is a straight-line estimate. Real weight change is uneven and usually slows, and daily calories are only estimates. Check your progress every few weeks and adjust, rather than relying on a fixed date.
Should I eat less or exercise more to create the deficit?
Either, or a mix, works. Your activity level is already included in your maintenance calories, so do not count the same exercise twice. Keeping protein up and doing some strength training can help you keep muscle. See our protein calculator.
Who should not use a calorie deficit calculator?
People under 18, who are pregnant or breastfeeding, who have a medical condition, or who have had an eating disorder should get personal advice from a doctor or registered dietitian. This calculator also refuses goals that would give a BMI below 18.5.
Disclaimer and editorial note
For information only, not medical advice. This calculator gives general estimates from the numbers you enter. It cannot diagnose, treat or prevent any condition and does not replace advice from a doctor, midwife, registered dietitian or other qualified professional who knows your history.
Written and maintained by the HealthFitnessHQ editorial team. We name the source of every formula and category used, and we review each calculator when guidance changes. Read how we work in our editorial policy and methodology.