How to Set a Calorie Deficit
A step by step method for setting a deficit: estimate maintenance, pick a rate you can hold, set protein, and adjust from real data rather than guesswork.
Last updated: 1 July 2026
Overview
Setting a deficit is four decisions: how many calories you burn, how big a gap to create, how much protein to eat, and what triggers a change.
Most people get the first one from a calculator, ignore the rest, and then wonder why it stopped working in week five.
Quick Answer
To set a calorie deficit, estimate your maintenance calories, subtract 15 to 25 percent, set protein at roughly 1.6 to 2.2g per kg of bodyweight, and adjust only after two weeks of consistent data showing you are not losing at your target rate.
Key Points
- Calculators give a starting estimate, not a truth.
- A 15 to 25 percent deficit suits most people.
- Protein goes up, not down, when calories come down.
- Two weeks of data before any adjustment.
- Daily steps are the easiest lever after food.
Step one: estimate maintenance
Use a calculator to get a starting number, then treat it as a hypothesis. A quick estimate that works reasonably well:
| Activity level | Calories per kg bodyweight |
|---|---|
| Sedentary desk job | 28 to 30 |
| Lightly active | 30 to 33 |
| Active job or 4 plus training days | 33 to 37 |
| Very active | 38 plus |
An 80kg person with a desk job and three gym sessions a week lands around 2400 calories. That is a starting point to test, not a fact about their body.
Better still: track what you currently eat for two weeks while your weight is stable. Whatever that averages is your actual maintenance.
Step two: choose the deficit
| Deficit | Weekly loss | Suits |
|---|---|---|
| 10 to 15 percent | Slow | Already lean, or prioritising performance |
| 15 to 20 percent | Moderate | Most people, most of the time |
| 20 to 25 percent | Faster | Higher body fat, short focused phase |
| Over 25 percent | Aggressive | Rarely worth it outside medical supervision |
For the 80kg example at 2400 maintenance, a 20 percent deficit is around 1900 calories.
Step three: set protein and fat
Protein first, because it protects muscle and controls hunger.
| Nutrient | Target |
|---|---|
| Protein | 1.6 to 2.2g per kg bodyweight |
| Fat | At least 0.6g per kg, for hormones and satiety |
| Carbohydrate | Whatever calories remain |
At 80kg and 1900 calories: 160g protein (640 cal), 60g fat (540 cal), leaving about 720 calories, or 180g, of carbohydrate.
Carbohydrate is the flexible one. It fuels training, so cutting it to zero makes sessions worse without making fat loss faster.
Step four: decide what triggers a change
Write the rule before you need it.
| Two week result | Action |
|---|---|
| Losing at target rate | Change nothing |
| Losing faster than target | Add 100 to 150 calories |
| Not losing, tracking honestly | Cut 100 to 150 calories or add 1000 daily steps |
| Weight flat but waist shrinking | Change nothing, it is working |
Adjust one thing at a time, and give it another two weeks. Changing calories every few days generates noise, not progress.
Diet breaks
Long deficits get harder, both physically and mentally. Planning a week at maintenance every 8 to 12 weeks is not falling off the wagon, it is maintenance practice, and it makes the next block easier.
Common Mistakes
| Mistake | Why it causes problems | Better approach |
|---|---|---|
| Trusting the calculator absolutely | It is an estimate with wide error bars | Adjust from real weight data |
| Cutting protein along with calories | Loses muscle and increases hunger | Raise protein as calories fall |
| Not tracking weekends | Undoes the weekday deficit | Track all seven days |
| Adjusting after three days | Noise, not signal | Wait two weeks |
| Cutting fat to near zero | Hormones and satiety suffer | Keep at least 0.6g per kg |
Frequently Asked Questions
How many calories should I cut?
Usually 15 to 25 percent below maintenance. In absolute terms that is often 300 to 600 calories a day for most adults.
Should I eat back the calories I burn in the gym?
Generally no. Fitness tracker estimates of exercise burn are unreliable and usually too high. Set your target based on your overall activity level and adjust from actual results.
What if I stop losing weight?
Check your tracking honestly for a week first. Most stalls are unlogged food or a drop in daily movement rather than metabolic adaptation.
How long should a fat loss phase last?
Typically 8 to 16 weeks, then a period at maintenance. Indefinite dieting is where adherence goes to die.
Sources
NHS weight loss guidance - https://www.nhs.uk/live-well/healthy-weight/
British Dietetic Association food facts - https://www.bda.uk.com/food-health/food-facts.html