How to use the Weight Loss & Calorie Deficit Calculator
- Choose kilograms or pounds and enter your current and goal weight.
- Enter the number of weeks you want to take.
- Enter your maintenance calories, the amount that keeps your weight steady. Use the BMR calculator on this site as a starting point.
- Read the daily deficit, the calories to eat and the weekly loss, and check the note.
Formula used
About 7,700 kcal equal 1 kg of body fat (3,500 kcal per lb). Daily deficit = weight to lose × 7,700 ÷ (weeks × 7). Daily calories = maintenance − deficit. Real weight change varies from person to person.
Worked example
Here is the Weight Loss & Calorie Deficit Calculator worked through with the example values shown above, so you can check each step by hand.
| Inputs | |
|---|---|
| Weight unit | Kilograms |
| Current weight | 80 |
| Goal weight | 72 |
| Time to reach it | 16 weeks |
| Maintenance calories per day | 2,400 kcal |
| Result | |
| Daily calorie deficit needed | 550 |
| Daily calories to eat | 1,850 |
| Weight loss per week | 0.5 kg per week |
| What it means | This pace is within a commonly suggested range for most adults. |
Daily deficit for different timeframes
The default goal of losing 8 kg, with only the weeks changed.
| Time to reach it | Daily calorie deficit needed | Weight loss per week |
|---|---|---|
| 8 weeks | 1,100 | 1 kg per week |
| 12 weeks | 733 | 0.67 kg per week |
| 16 weeks | 550 | 0.5 kg per week |
| 24 weeks | 367 | 0.33 kg per week |
| 32 weeks | 275 | 0.25 kg per week |
How the numbers are worked out
A common estimate is that about 7,700 calories equal 1 kg of body fat, or 3,500 calories per pound. To lose 8 kg (from 80 kg to 72 kg) you need a total deficit of about 61,600 calories. Over 16 weeks (112 days), that is 550 calories a day. With maintenance calories of 2,400, you would eat about 1,850 calories a day.
The loss comes to 0.5 kg per week. Slower, steadier loss is easier to keep up, and faster loss makes you hungrier and harder to sustain.
Timeframe changes the deficit
For the same 8 kg: in 8 weeks the deficit is 1,100 calories a day, in 12 weeks 733, in 24 weeks 367 and in 32 weeks 275. A shorter timeframe needs a bigger deficit, and at some point the calorie target becomes unrealistically low.
The calculator warns you when the calories to eat fall very low or when the weekly loss is faster than about 1% of body weight.
Why real results differ
The 7,700 calorie figure is an average, not a law. As you lose weight, your body needs fewer calories, so the same intake gives a smaller deficit over time. Water weight, muscle changes and measurement errors in food and exercise tracking all add noise. Expect progress to be uneven from week to week.
Use the result as a starting plan and adjust it after a few weeks based on what the scale and your measurements really do. If you are not losing, reduce intake a little or increase activity.
Safety and good habits
Many health organisations suggest a gradual pace of roughly 0.25 to 1 kg (0.5 to 2 lb) a week for most adults. Very low calorie intakes can cause nutrient shortages and muscle loss, and they are not suitable for everyone. If you have a medical condition, are pregnant or breastfeeding, are under 18 or have a history of disordered eating, speak to a doctor or dietitian before changing your diet.
This calculator gives general information and is not medical advice. Combine a moderate deficit with enough protein, regular activity and good sleep, and be patient.
Frequently asked questions
Is the 7,700 calories per kg rule exact?
No. It is a rough average. The body adapts as you lose weight, so progress is rarely perfectly linear.
What is a safe rate of weight loss?
Many health bodies suggest roughly 0.25 to 1 kg (0.5 to 2 lb) per week, depending on your weight. Talk to a doctor or dietitian, especially if you have a health condition.
How do I find my maintenance calories?
Estimate them from your BMR and activity level, or track your food and weight for a few weeks until your weight stays steady.
What if the calories to eat are very low?
Choose a longer timeframe. Very low intakes are hard to sustain and may not be safe without medical advice.
Does exercise count towards the deficit?
Yes. You can create the deficit by eating less, moving more or both. If you add exercise, you can eat a little more and keep the same deficit.
Why am I not losing weight as predicted?
Common reasons are underestimated food intake, overestimated activity, water retention and a lower maintenance level than you assumed. Adjust the plan using real results.
This calculator gives estimates for information only. Actual figures from a bank, employer, tax authority or doctor may differ. It is not financial, tax, legal or medical advice.