Kilojoule Deficit Calculator
A kilojoule deficit is the difference between what you eat and what your body needs. This calculator shows your deficit and translates it into predicted weekly weight loss.
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How It Works
Your deficit = maintenance kJ - daily intake kJ. One kilogram of body fat stores approximately 32,200 kJ. Your weekly deficit divided by 32,200 gives the predicted weekly weight loss in kg.
Quick Reference
| Daily Deficit (kJ) | Weekly Loss (kg) | Monthly Loss (kg) |
|---|---|---|
| 1,150 | 0.25 | ~1.0 |
| 2,300 | 0.50 | ~2.0 |
| 3,450 | 0.75 | ~3.0 |
| 4,600 | 1.00 | ~4.0 |
Assumes consistent deficit. Actual results vary with metabolic adaptation.
How This Is Calculated
- maintenance kJ
- = your TDEE (BMR × activity multiplier)
- daily intake kJ
- = the kilojoules you eat per day
- 32,217
- = kJ stored in 1 kg of body fat
A safe deficit is 2,000–3,000 kJ (500–750 kcal) per day, resulting in weight loss of 0.5–0.75 kg per week. Larger deficits can lead to muscle loss.
Frequently Asked Questions
- What is a safe kilojoule deficit?
- A safe deficit is 2,000-3,000 kJ (500-750 kcal) per day, resulting in weight loss of 0.5-0.75 kg per week. Larger deficits can lead to muscle loss, nutritional deficiencies, and metabolic adaptation.
- How do I know my current kJ intake?
- Track everything you eat and drink for a week using a food diary or tracking app. Read Australian food labels (which show kJ) and weigh portions for accuracy. Our Food Diary tool can help.
- Why am I not losing weight in a deficit?
- Common reasons include: underestimating food intake, overestimating exercise burn, water retention (especially early on), metabolic adaptation from prolonged dieting, or medical conditions. If stuck, recalculate your maintenance kJ and track intake more carefully.
Related Tools
kJ Per Day to Lose Weight Calculator
Calculate how many kilojoules per day you should eat to lose weight at a safe, sustainable rate.
Calorie Deficit Calculator
Calculate your optimal calorie deficit for weight loss. See how long it will take to reach your goal weight with a safe, sustainable deficit.
Daily Energy Needs Calculator
Calculate your daily energy requirement in kilojoules using the Harris-Benedict formula based on age, weight, height, and activity level.