A calorie deficit means eating fewer calories than your body burns, so the difference comes from stored fat — the mechanism behind every effective diet. A 500-calorie daily deficit loses roughly half a kilogram per week. This free calculator finds your maintenance calories and sizes a safe deficit for your goal, with a realistic timeline.
Every diet that has ever worked — keto, fasting, points, shakes — worked for the same unglamorous reason: it created a calorie deficit. Eat fewer calories than your body burns and stored fat makes up the difference; there is no second mechanism. This calorie deficit calculator sizes that gap for your body and goal, and the guide below answers the questions that decide success: what a calorie deficit actually is, how to calculate yours, how many calories you should eat to lose weight, and how fast the scale can realistically move.
Weight-Loss Timeline
Estimate how long to reach your goal at a given daily deficit.
What is a calorie deficit?
A calorie deficit means consuming less energy than your body expends. Your body must cover the shortfall from its reserves — primarily body fat — which is precisely the goal of fat loss. The reference point is your total daily energy expenditure (TDEE): eat at TDEE and your weight holds; eat below it and you lose. Because roughly 7,700 calories correspond to one kilogram of body fat (about 3,500 per pound), the size of your daily deficit sets the pace of loss with almost arithmetic reliability over the medium term.
How to calculate your calorie deficit
Three steps, all of which the calculator automates:
- 1. Find your TDEE. Your maintenance calories, estimated from age, sex, height, weight and activity — see our TDEE calculator for the full method.
- 2. Choose a deficit size. Moderate wins for most people: 300–500 calories below maintenance. Larger deficits trade muscle, energy and adherence for speed.
- 3. Eat to the target and verify with the scale. The weekly weight trend — not any formula — is the final word; adjust by 100–200 calories if the trend disagrees with the plan.
How many calories should I eat to lose weight?
There is no universal number — only your maintenance minus a sensible gap. Worked examples at a 500-calorie deficit:
| Profile | Estimated TDEE | Target intake | Expected pace |
|---|---|---|---|
| Woman, 35, 70 kg, lightly active | ~2,000 kcal | ~1,500 kcal | ~0.5 kg/week |
| Man, 40, 90 kg, lightly active | ~2,600 kcal | ~2,100 kcal | ~0.5 kg/week |
| Woman, 55, 62 kg, sedentary | ~1,700 kcal | ~1,300 kcal | ~0.4 kg/week |
| Man, 28, 105 kg, moderately active | ~3,200 kcal | ~2,700 kcal | ~0.5 kg/week |
Notice what these examples imply: a fixed prescription like 1,200 calories is far too low for some people and pointlessly harsh for most. Anchor your intake to your own expenditure, not to a number borrowed from someone else’s diet.
500 calorie deficit vs 1000: choosing your pace
| Daily deficit | Weekly loss | Best suited to | Trade-offs |
|---|---|---|---|
| 250–300 kcal | ~0.25 kg | Lean people, last few kilos, minimal hunger | Slow but very sustainable |
| 500 kcal | ~0.5 kg | Most people, most of the time | The evidence-backed default |
| 750–1000 kcal | ~0.75–1 kg | Higher starting weights, medical urgency | More hunger, muscle risk — best with professional support |
Whatever the size, protect the quality of the loss: keep protein around 1.6–2.2 g per kilogram of body weight and keep training your muscles — our macro calculator turns the calorie target into a complete plan.
How long to lose 20 pounds — or any amount
Divide the fat you want to lose by your weekly pace: 20 pounds (about 9 kg) at half a kilogram per week is roughly 18 weeks — four to five months. Plan for plateaus and holidays and it is closer to six. This arithmetic is worth doing before you start: it sets expectations that survive contact with real life, which is what separates finished diets from abandoned ones. Rapid alternatives exist mainly in marketing; a deficit your life can absorb wins on every horizon beyond a month.
Why the scale stalls in a calorie deficit
- Water masks fat. Salt, carbs, new training and hormonal cycles swing water weight by 1–2 kg; a flat scale for ten days can still hide steady fat loss underneath. Judge two-to-three-week trends, never single days.
- Intake creeps. Oils, sauces, bites and drinks add hundreds of untracked calories. If loss stops, tighten measurement before cutting deeper.
- Expenditure adapts. A smaller body burns less, and metabolism economises modestly during long diets. Recalculate your TDEE after every ~5 kg lost.
- The estimate was off. Every calculator carries ±10%; the scale trend is your correction signal.
Calorie deficit safety: when to involve a doctor
A moderate deficit is safe for most healthy adults. Get medical guidance first if you have diabetes or use glucose-lowering medication, have thyroid, kidney, liver or heart disease, are pregnant or breastfeeding, are under 18, or have any history of disordered eating. And treat weight loss you did not plan as a symptom to investigate, never a bonus. Sustained very-low-calorie diets belong under clinical supervision — for severe obesity, structured programs including bariatric and metabolic options exist precisely because willpower is not the missing ingredient.
This tool is informational. It does not diagnose any condition or replace personalised advice from a clinician or dietitian.
Frequently asked questions
What is a calorie deficit in simple terms?
Eating fewer calories than your body burns in a day, so the difference is drawn from stored fat. It is the mechanism behind every effective weight-loss diet.
Is a 1,200-calorie diet a good calorie deficit?
Only coincidentally. 1,200 is an arbitrary number that ignores your actual expenditure — for many adults it means an unnecessarily aggressive deficit. Set the gap relative to your own TDEE instead.
Can I be in a calorie deficit and not lose weight?
Not over weeks — physics holds. What happens in practice is that water retention hides the loss short-term, or the deficit was smaller than believed due to untracked calories or an overestimated activity level.
Do I need to cut carbs to lose weight?
No. Low-carb, low-fat and balanced diets produce equivalent fat loss when calories and protein match. Choose the eating pattern you can maintain; the deficit does the work.
Should I eat back exercise calories?
No — your activity level already covers typical training. Eating back workout estimates (which devices routinely inflate) is one of the fastest ways to erase a deficit.
How big is too big a calorie deficit?
Beyond ~1,000 calories a day, muscle loss, fatigue and rebound risk climb quickly; long-term intakes at or below your BMR deserve professional supervision. If you feel weak, dizzy or preoccupied with food, the deficit is too aggressive.
Will a calorie deficit slow my metabolism?
Expenditure falls modestly as you get lighter and your body economises — a normal adaptation, not damage. Keeping protein high, lifting weights and taking occasional diet breaks limits it.
Numbers are a starting point — not a diagnosis
If your results raise questions, Acibadem specialists can review your situation properly: share your case and receive a free, no-obligation medical opinion from the relevant department.