Complete guide
Reviewed July 2026Weight loss comes down to one principle: a calorie deficit. Eat fewer calories than your body burns, and it makes up the difference by drawing on stored fat. Every diet that works - low-carb, intermittent fasting, portion control - works because it creates a deficit, whether or not it says so. Understanding the deficit directly lets you plan loss instead of chasing the latest trend.
This calculator sizes your daily deficit from your maintenance calories (TDEE) and your goal loss rate, and shows the intake to hit it. Below you'll find the deficit-to-loss math, worked examples, safe limits, why the scale doesn't move in a straight line, and the mistakes that stall progress.
The goal isn't the biggest possible deficit - it's the largest one you can sustain while keeping muscle and energy. Slow and steady genuinely wins here.
How a calorie deficit becomes weight loss
Deficit = TDEE - calorie intake Weekly fat loss (kg) = (daily deficit x 7) / 7700 1 kg of body fat stores about 7,700 kcal Daily intake = TDEE - target deficit
One kilogram of body fat holds roughly 7,700 kcal of energy. So a 500 kcal daily deficit adds up to 3,500 kcal a week - about 0.45 kg of fat. Double the deficit and you roughly double the rate, but you also raise the risk of losing muscle and stalling. The deficit is the lever; the 7,700 figure converts it to kilograms.
Worked examples
- TDEE 2,200 kcal, 500 deficit: eat 1,700 kcal/day; weekly loss = 500 x 7 / 7700 = about 0.45 kg.
- TDEE 2,800, 750 deficit: eat 2,050; weekly loss = 750 x 7 / 7700 = about 0.68 kg.
- Goal-driven: to lose 6 kg in 12 weeks = 0.5 kg/week, needing a ~550 kcal daily deficit.
- Minimum floors: don't drop below ~1,200 kcal (women) or ~1,500 (men) without medical guidance.
Choosing a safe deficit
| Deficit/day | Weekly loss | Best for | Risk |
|---|---|---|---|
| 250 kcal | ~0.23 kg | Small amounts to lose, easy to sustain | Slow |
| 500 kcal | ~0.45 kg | Most people - the standard | Low |
| 750 kcal | ~0.68 kg | More to lose, disciplined | Some muscle/energy risk |
| 1000 kcal | ~0.9 kg | Short-term, supervised | Muscle loss, fatigue, rebound |
Why the scale doesn't move in a straight line
Fat loss is steady, but scale weight isn't - it swings daily with water, food in the gut, sodium, hormones and glycogen. You can be in a real deficit and see the scale rise for days, then drop suddenly (a 'whoosh'). This is why you should judge progress by the weekly average trend over 2-3 weeks, not any single morning's number.
Using this calculator
- Enter your maintenance calories (TDEE) - use the TDEE or calorie calculator if you don't know it.
- Choose a target loss rate or deficit size; 0.5 kg/week (about 500 kcal) suits most people.
- Read your daily intake target and expected weekly loss.
- Track weight as a weekly average and adjust intake by 100-200 kcal if the trend doesn't match after 2-3 weeks.
Common mistakes
- Setting too aggressive a deficit, then losing muscle, stalling, and rebounding.
- Not eating enough protein, so a chunk of the loss is muscle rather than fat.
- Judging progress by daily scale readings instead of the weekly trend.
- Forgetting that TDEE falls as you lose weight - the same deficit shrinks over time, so recalculate.
- Under-counting intake: liquid calories, cooking oil and 'bites' quietly erase the deficit.
Frequently asked questions
Glossary
- Calorie deficit
- Eating fewer calories than you burn, causing weight loss.
- TDEE
- Total Daily Energy Expenditure - your maintenance calories.
- 7,700 kcal rule
- The approximate energy stored in 1 kg of body fat.
- Maintenance calories
- The intake that holds weight steady - equal to TDEE.
- Muscle preservation
- Keeping muscle during a deficit via protein and resistance training.
- Metabolic adaptation
- The fall in energy use that can follow prolonged dieting.
- Weekly trend
- The average weight over a week - the true measure of fat loss.
- Diet break
- A planned period at maintenance to aid adherence during long diets.
Key takeaways
A calorie deficit - eating below your TDEE - is the engine of all weight loss, and 1 kg of fat is about 7,700 kcal, so a 500 kcal daily deficit loses roughly 0.45 kg/week. Choose the largest deficit you can sustain while eating 1.6-2.2 g/kg protein and lifting to keep muscle, ignore daily scale noise in favour of the weekly trend, and recalculate as your lighter body's TDEE falls. Moderate and consistent beats aggressive and short-lived.
Enter your maintenance calories and goal above for your daily intake target; then track your weekly-average weight and fine-tune by 100-200 kcal from the real trend.