Free calculator

kJ Per Day to Lose Weight Calculator

Find out exactly how many kilojoules you should eat per day to reach your weight loss goal. Enter your details and desired rate of weight loss, and this calculator will give you a daily kJ target.

Enter your details

Gender

Age

years

Weight

Height

Activity Level

Weight Loss Rate

Your Weight Loss Plan

Example

Example figures, not your own. Worked for a moderately active 35 year old woman of 75 kg and 165 cm losing 0.5 kg a week. Enter your own details and press Calculate.

Daily kJ Target

7,431kJ/day

To lose 0.5 kg per week

Daily Deficit

2,301kJ

Below your maintenance level

Maintenance Level

9,733kJ/day

How It Works

First, your maintenance energy is calculated using the Harris-Benedict formula. Then, a deficit is applied based on your target weekly weight loss. One kilogram of body fat contains approximately 32,200 kJ (7,700 kcal). To lose 0.5 kg per week, you need a daily deficit of about 2,300 kJ.

How to use it

1Enter your gender, age, weight, height, and activity level
2Select your target weight loss rate (0.25, 0.5, 0.75, or 1.0 kg per week)
3Click "Calculate" to see your daily kJ target

Quick Reference

Goal	Daily Deficit (kJ)	Weekly Deficit (kJ)
0.25 kg/week	1,150	8,054
0.50 kg/week	2,300	16,109
0.75 kg/week	3,450	24,163
1.00 kg/week	4,600	32,217

1 kg of body fat ≈ 32,217 kJ (7,700 kcal) of stored energy.

How This Is Calculated

Daily deficit (kJ) = (target weekly loss in kg × 32,217) ÷ 7 Target intake (kJ) = maintenance kJ − daily deficit

32,217 kJ: = energy stored in 1 kg of body fat (7,700 kcal × 4.184)
maintenance kJ: = your TDEE (BMR × activity multiplier)

This is a simplified energy balance model. Actual weight loss depends on metabolic adaptation, water retention, and body composition changes.

Frequently Asked Questions

How many kJ per day to lose 1 kg per week?

To lose 1 kg per week, you need a daily deficit of approximately 4,600 kJ (1,100 kcal) below your maintenance level. For most people, this means eating around 5,000-6,500 kJ per day, depending on activity level. Note: losing more than 0.5-1 kg per week is generally not recommended.

How many kilojoules per day to lose weight for a woman?

Most women can lose weight eating 5,000-6,500 kJ per day, depending on their size and activity level. It's generally not recommended to go below 5,000 kJ (1,200 kcal) per day without medical supervision.

Is 5000 kJ a day enough?

5,000 kJ (about 1,200 calories) is a low but manageable intake for many women aiming for weight loss. For men, this is typically too low. The minimum safe intake depends on your body size and should be discussed with a healthcare provider.

How many kilojoules per day to lose 1 kg per week?

You need a daily kJ deficit of approximately 4,600 kJ below maintenance. If your maintenance is 8,700 kJ, you'd need to eat about 4,100 kJ per day - which is quite restrictive. A more sustainable approach is losing 0.5 kg per week (deficit of ~2,300 kJ/day).

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