A calorie deficit means eating fewer calories than your body burns in a day. It is the single thing that causes weight loss, every diet works by creating one, whether it counts calories or not. To be in a deficit, eat about 300 to 500 calories below the amount you burn (your TDEE), move more, or both. Here is how it works.
What counts as a calorie deficit?
Your body burns a certain number of calories a day to stay alive and move around, called your TDEE (Total Daily Energy Expenditure). Eat below that number and the gap is your deficit, so your body makes up the difference from stored fat. Eat at it and you maintain. Eat above it and you gain.
How big should a calorie deficit be?
Big enough to make progress, small enough to sustain. About 7700 calories equals 1 kg of fat, so:
| Daily deficit | Weekly loss (approx) | Sustainability |
|---|---|---|
| 250 kcal | 0.25 kg | Very easy, slow |
| 500 kcal | 0.5 kg | Steady, recommended |
| 750 to 1000 kcal | 0.75 to 1 kg | Hard, risks muscle loss |
For most people a 500 calorie deficit is the sweet spot. Aggressive deficits lose faster but are harder to hold and can cost you muscle, which is why crash diets rebound.
Work out your deficit
Calorie deficit calculator
Maintenance calories (your TDEE)
Sex
Target loss per week
EAT THIS MANY CALORIES A DAY
1,950 kcal
-550
daily deficit
0.5 kg
per week
Keep protein high so the deficit stays comfortable, and judge progress on the multi-week scale trend.
Let forme hold the deficit for you
forme sets a safe deficit from your goal and tracks your day from a scan, so you stay in it without counting every gram.
How do you create a calorie deficit?
Three levers, ideally a mix:
- Eat a bit less, especially of calorie-dense, easy-to-overeat foods.
- Choose more filling foods, so the deficit does not feel like one. Protein, fibre and less processed foods keep you fuller per calorie.
- Move more, which raises the calories you burn so you can eat more and still be in a deficit.
Can you be in a deficit without counting calories?
Yes. Counting is one way to find a deficit, not the only way. You can lean on portion habits, higher-protein and less processed choices, and a target you track loosely rather than a daily ledger. The deficit still has to be there, you just create it with habits instead of a spreadsheet.
Why am I in a deficit but not losing weight?
Usually one of three things: you are eating more than you think (easy to do), water weight is masking fat loss on the scale, or you are reading day-to-day noise instead of the trend. Look at the scale trend over two to three weeks. If it is flat, tighten the deficit by 100 to 150 calories.
Your deficit, worked out for you
forme calculates the calories you burn, builds in a safe deficit for your goal, and tracks your day from a scan so the deficit takes care of itself.
How forme handles it
forme works out your maintenance calories from your stats, applies a sensible deficit for your goal and pace, and gives you a daily target with protein, carbs and fat. Then it tracks your day from a quick scan and leads with a personal food score, so you naturally lean towards the filling, less processed choices that make a deficit easy to hold.
The bottom line
A calorie deficit is eating below what you burn, and it is what drives all weight loss. Aim for around 500 calories below your TDEE, get there with filling foods and a bit more movement, and judge progress by the trend rather than the day. This is food guidance to help you reach your own goals, not medical or dietary advice.