Calorie deficit: what it is and how to calculate it to lose weight
Every way of losing weight works for the same reason: a calorie deficit. We explain what it is, how to work out yours, how much weight to expect to lose and how to keep it up without going hungry.
Key takeaways
- You lose weight when you eat fewer calories than you burn.
- A 15–20% deficit is a good starting point.
- A pace of 0.5 to 1 kg a week is the most recommended.
- Look at the trend over weeks, not one day’s weight.
Article contents
What is a calorie deficit?
It means eating fewer calories than you burn. When that happens, your body uses its stores to cover the gap, and over time you lose weight. No diet works without it: fasting, low carb or anything else, they all lose weight because they create a deficit.
How to calculate your deficit
- Work out your maintenance calories with our calorie calculator.
- Take away 15 to 20%. That is your daily target.
Example: with 1,953 maintenance calories, a 15% deficit gives a target of 1,660 kcal, or 293 kcal less a day.
| Deficit | Fewer calories | What to expect |
|---|---|---|
| Small | 10% | Slow and easy to sustain |
| Moderate | 15–20% | The most common starting point |
| Large | Over 25% | More hunger and more risk of losing muscle |
How much weight will you lose?
A common approximation is that a kilogram of fat holds about 7,700 kcal. With 293 kcal less a day, the person in the example would lose about 0.27 kg a week at first.
Health services usually recommend 0.5 to 1 kg a week. Faster is harder to sustain and increases muscle loss.
How to keep a deficit without going hungry
- Eat enough protein. It is filling and protects your muscle. See how much you need in our protein guide.
- Fill your plate with vegetables. They add volume with few calories.
- Watch your drinks. Soda, juice and alcohol add lots of calories without curbing hunger.
- Log what you eat. It is the most reliable way to know you are really in a deficit.
- Sleep well. Short sleep increases appetite.
If you stop losing weight
As you lose weight, your body burns a little less. If nothing has changed for three or four weeks, recalculate your calories with your new weight and check that your log is complete: oils, dressings and drinks are often forgotten.
Frequently asked questions
How big should a calorie deficit be?
Eating 15 to 20% less than your maintenance calories is a good starting point for most people.
How much weight do you lose with a 500 calorie deficit?
Using the approximation of 7,700 kcal per kilogram of fat, about 0.45 kg a week at first. The pace usually slows over time.
Can you lose weight without counting calories?
Yes, if you eat less than you burn. Counting calories isn’t required, but it is the most reliable way to know you are in a deficit.
Why am I not losing weight in a deficit?
The most common reasons are underestimating what you eat or water swings in your weight. Check your log and look at the trend over 3 or 4 weeks.
Sources
- NHS. Lose weight — Better Health. www.nhs.uk/better-health/lose-weight/
- Mifflin MD, St Jeor ST, et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241-247. doi.org/10.1093/ajcn/51.2.241
- World Health Organization. Healthy diet — Fact sheet. www.who.int/news-room/fact-sheets/detail/healthy-diet
We write nutrition guides with the same calculations and sources the app uses, cited at the end of each article.
This content is for information only and does not replace advice from a doctor or dietitian. If you have a health condition, are pregnant or take medication, check with a professional before changing how you eat.
