What is a safe calorie deficit?

A safe calorie deficit is generally 2,000-3,000 kJ (500-750 kcal) per day, which leads to weight loss of 0.5-0.75 kg per week. The NHMRC recommends against losing more than 1 kg per week for most adults, as faster loss increases the risk of muscle loss and nutritional deficiencies.

Why is my weight loss slowing down?

As you lose weight, your body requires fewer kilojoules to function (lower BMR and TDEE). This means the same calorie intake that created a deficit initially may only maintain your new weight. Recalculate your targets every 5 kg lost to stay on track.

Can I just eat 1,200 calories to lose weight faster?

Very low calorie diets (below 5,000 kJ or 1,200 kcal for women, 6,300 kJ or 1,500 kcal for men) should only be followed under medical supervision. They can lead to muscle loss, nutrient deficiencies, gallstones, and metabolic adaptation that makes future weight loss harder.

Should I eat back the calories I burn from exercise?

It depends on your goal. If your TDEE already accounts for your exercise level, you do not need to eat back exercise calories. If you calculated your TDEE at sedentary and exercise on top, you may eat back 50-75% of exercise calories to avoid too large a deficit.

Calorie Deficit Calculator

Work out the exact calorie deficit you need to reach your goal weight safely. This calculator shows your maintenance calories, recommended deficit, daily intake target, and an estimated timeline to reach your goal.

Enter Your Details

Gender

Age

years

Current Weight

Height

Activity Level

Goal Weight

Deficit Level

How It Works

Your maintenance calories are calculated using the Mifflin-St Jeor equation multiplied by your activity factor. The deficit is the difference between your maintenance level and your target intake. Since approximately 7,700 kcal (32,200 kJ) equals one kilogram of body fat, your weekly weight loss is determined by your daily deficit multiplied by 7, divided by 7,700.

Quick Reference

Deficit Level	Deficit	Weekly Loss	Time to Lose 10 kg
Mild (10%)	~800 kJ/day	~0.25 kg	~40 weeks
Moderate (20%)	~1,600 kJ/day	~0.5 kg	~20 weeks
Aggressive (25%)	~2,100 kJ/day	~0.75 kg	~14 weeks
Extreme (30%)	~2,500 kJ/day	~1.0 kg	~10 weeks

Approximate values for a person with 8,400 kJ/day maintenance. Actual results vary by individual.

Frequently Asked Questions

What is a safe calorie deficit?: A safe calorie deficit is generally 2,000-3,000 kJ (500-750 kcal) per day, which leads to weight loss of 0.5-0.75 kg per week. The NHMRC recommends against losing more than 1 kg per week for most adults, as faster loss increases the risk of muscle loss and nutritional deficiencies.
Why is my weight loss slowing down?: As you lose weight, your body requires fewer kilojoules to function (lower BMR and TDEE). This means the same calorie intake that created a deficit initially may only maintain your new weight. Recalculate your targets every 5 kg lost to stay on track.
Can I just eat 1,200 calories to lose weight faster?: Very low calorie diets (below 5,000 kJ or 1,200 kcal for women, 6,300 kJ or 1,500 kcal for men) should only be followed under medical supervision. They can lead to muscle loss, nutrient deficiencies, gallstones, and metabolic adaptation that makes future weight loss harder.
Should I eat back the calories I burn from exercise?: It depends on your goal. If your TDEE already accounts for your exercise level, you do not need to eat back exercise calories. If you calculated your TDEE at sedentary and exercise on top, you may eat back 50-75% of exercise calories to avoid too large a deficit.

How This Is Calculated

Maintenance (kcal) = BMR × Activity Factor Deficit (kcal) = Maintenance × Deficit % Target Intake (kcal) = Maintenance − Deficit Weekly Loss (kg) = (Deficit × 7) ÷ 7,700

BMR: = Basal Metabolic Rate from Mifflin-St Jeor equation
Activity Factor: = 1.2 (sedentary) to 1.9 (very active)
7,700: = Approximate kcal in 1 kg of body fat

The 7,700 kcal per kg figure is an average. Actual fat loss may differ due to water retention, metabolic adaptation, and changes in lean mass.

Related Tools

TDEE Calculator

Calculate your Total Daily Energy Expenditure using the Mifflin-St Jeor equation. See how many calories and kilojoules you burn per day.

Calorie Calculator

Calculate how many calories and kilojoules you need per day to lose, maintain, or gain weight. Personalised to your body and activity level.

Weight Loss Calculator

Calculate how long it will take to reach your goal weight. See weekly milestones and the daily calorie target needed.

Disclaimer

This calculator provides estimates for informational purposes only and should not be considered medical advice. Individual results may vary based on factors not captured by these formulas. Consult a healthcare professional before making changes to your diet or exercise routine, especially if you have any existing health conditions.