Calorie Deficit Calculator for Australians
Work out how many kilojoules (or Calories) to eat each day to reach your goal weight. Metric units, Aussie-friendly kJ, and nothing leaves your device.
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Time to reach goal
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What is a calorie deficit?
A calorie deficit means eating fewer kilojoules than your body burns. Your body makes up the difference from stored energy, mostly body fat. Because about 7,700 Cal (32,200 kJ) is stored in 1 kg of fat, a daily deficit of roughly 550 Cal (2,300 kJ) leads to about 0.5 kg of loss per week.
How to use this calculator
- Enter your sex, age, height, current weight and goal weight in metric.
- Pick the activity level that matches a typical week.
- Choose a pace. Steady (0.5 kg a week) suits most people.
- Switch between kJ and Cal using the toggle on the results card.
Tips for a sustainable deficit
- Prioritise protein and fibre to stay full on fewer kilojoules.
- Weigh yourself at the same time each week and look at the trend, not single days.
- Re-run the calculator every 5 kg lost as your energy needs fall.
- See the Australian Dietary Guidelines for balanced eating advice.
Want to understand the maths? Read how the calculator works.
More tools and guides
Frequently asked questions
How many calories (kilojoules) should I cut to lose weight?
A deficit of about 500 Cal (roughly 2,100 kJ) a day is a common starting point and leads to around 0.5 kg of fat loss per week. Smaller deficits are easier to maintain and help protect muscle.
Does this calculator use kilojoules or Calories?
Both. Australian food labels list energy in kilojoules (kJ), so the calculator defaults to kJ. One Calorie (kcal) equals 4.184 kJ, and you can switch units with a single tap.
How is my daily energy need calculated?
We estimate your Basal Metabolic Rate (BMR) with the Mifflin-St Jeor equation, then multiply it by an activity factor to get your Total Daily Energy Expenditure (TDEE). Your target intake is your TDEE minus the deficit needed for your chosen pace.
What is a safe rate of weight loss?
Most health guidance suggests 0.25–1 kg per week. Losing faster than that increases the risk of muscle loss, fatigue and nutrient gaps. We never set a target below your estimated BMR or 1,200 Cal (5,020 kJ) for women and 1,500 Cal (6,276 kJ) for men.
Why does the 7,700 Cal per kg figure matter?
About 7,700 Cal (32,200 kJ) is the energy stored in 1 kg of body fat. It is a useful rule of thumb for planning, but real-world results vary because your metabolism adapts as you lose weight.
Is this calculator suitable for everyone?
No. It is designed for healthy adults aged 18 and over. It is not suitable for people who are pregnant, breastfeeding, have an eating disorder or have a medical condition affecting metabolism. Speak to your GP or an Accredited Practising Dietitian (APD) before starting a weight loss plan.
Why is my result different from other calculators?
Different calculators use different equations, activity multipliers and safety floors. Treat every estimate as a starting point, then adjust after 2–3 weeks based on how your weight actually changes.
Do you store my data?
No. All calculations run in your browser. Nothing you enter is sent to a server. Your last inputs are saved only on your own device so the form is pre-filled next time.