How the Calculator Works

The calculator follows the steps in the Nutrient Reference Values for Australia and New Zealand (Eat for Health).

1. It estimates your basal metabolic rate, the energy your body uses at rest, from your sex, age and weight, using the Schofield equations the Nutrient Reference Values are based on.
2. It multiplies that figure by an activity factor for your usual day. If you also do sport or strenuous exercise for 30 to 60 minutes, 4 to 5 times a week, it adds 0.3, as the Nutrient Reference Values suggest. It does not add this to heavy physical work or very active leisure, which already includes it. The result is roughly what your body uses now, and what many apps call maintenance calories.
3. If your BMI is 25 or more, it runs the same sum at a healthy weight for your height: a BMI of 22, about the middle of the healthy range of 18.5 to 24.9. That figure is your daily target, used as it is, with nothing further taken off.
4. The daily gap is the difference between the two. The weekly figure is the same gap times seven.

The calculator then checks two Australian figures. The Australian Obesity Management Algorithm (2024), a guide for primary care, puts a modest energy deficit at about 2,000 to 4,000 kJ a day (about 480 to 960 calories). That describes the size of the gap, not a further cut from your target. The Better Health Channel (Victorian Government) says a good weight management service will advise against a daily intake below 5,000 kJ (1,200 calories).

One calorie (kilocalorie) is about 4.2 kJ. The calculator rounds kilojoules to the nearest 100 and calories to the nearest 10. The calorie gap is the difference between the two rounded calorie figures, so the numbers add up.

A Worked Example

Take a woman aged 31 to 50 with seated work, 160 cm tall and weighing 79 kg:

• uses now: about 8,700 kJ (about 2,080 calories) a day
• target at 56.3 kg, a BMI of 22: about 7,600 kJ (about 1,820 calories) a day
• daily gap: about 1,100 kJ (about 260 calories)
• the same gap over a week: about 7,700 kJ (about 1,820 calories)

Her target sits well above the 5,000 kJ floor, and her gap sits below the 2,000 to 4,000 kJ range. As weight comes down, what the body uses comes down too, so the gap narrows over time. For the step by step method behind these figures, see what a calorie deficit is and how to work out yours.

Daily Gap and Weekly Gap

The chart shows how a daily energy gap adds up over a week. It is arithmetic only: it shows energy, not a change on the scale. Rates of weight loss vary widely between individuals.

• 500 kJ a day (about 120 calories)3,500 kJ a week (about 840 calories)
• 1,000 kJ a day (about 240 calories)7,000 kJ a week (about 1,680 calories)
• 1,500 kJ a day (about 360 calories)10,500 kJ a week (about 2,520 calories)
• 2,000 kJ a day (about 480 calories)14,000 kJ a week (about 3,360 calories)
• 2,500 kJ a day (about 600 calories)17,500 kJ a week (about 4,200 calories)

Arithmetic only. Outcomes vary between individuals.

What the Numbers Cannot Tell You

• The estimates are approximate. People of the same age, sex and size who seem equally active can still need very different amounts of energy. Small movements such as fidgeting make a big difference for some people.
• The equations probably over-estimate the energy older people use at rest.
• Physical activity is the part of energy use that varies most, and choosing an activity level is a judgement call.
• BMI cannot tell how much of your weight is muscle and how much is fat. It is less accurate for some high-performance athletes, body builders, people with a physical disability, and people from some ethnic groups, including Aboriginal and Torres Strait Islander peoples, Pacific Islanders, Maori people, and South Asian, Chinese and Japanese people. The Nutrient Reference Values also note that a somewhat higher BMI range of 22 to 27 may suit older people.
• The calculator is not suited to pregnancy or breastfeeding, when energy needs go up, or to anyone under 19.

Pair the Numbers With Healthy Eating and Physical Activity

A target is easier to reach with a healthy diet built on the five food groups: vegetables and legumes, fruit, grain foods (mostly wholegrain), lean meats and alternatives such as fish, eggs, tofu, nuts and legumes, and milk, yoghurt and cheese or their alternatives (mostly reduced fat). The Australian Dietary Guidelines also recommend limiting foods and drinks with saturated fat, added salt, added sugars and alcohol. To split your target into protein, carbohydrate and fat, see macros for weight loss.

Physical activity widens the gap and supports health in its own right. Australia's guidelines for adults suggest 30 minutes or more of moderate to vigorous physical activity on most days, plus muscle-strengthening activities on 2 or more days a week. For adults above a healthy weight, the NHMRC guidelines pair reduced intake with about 300 minutes of moderate activity, or 150 minutes of vigorous activity, each week. For ideas, see how many steps a day to lose weight and how to lose weight: a realistic guide.

To follow progress, look at the trend over several weeks rather than a single weigh-in, and see how to calculate your weight loss percentage. If the scale stalls, read why the scale may not move in a calorie deficit.

When to Get Personal Advice

If you have a health condition such as diabetes, heart disease or cancer, a fad diet can be especially risky, so talk to a GP or accredited practising dietitian before you start a new eating plan. A registered health practitioner can also help if diet and physical activity changes have not been enough for your health goals. Whether any treatment beyond diet and exercise suits you is a decision made after an individual assessment, and outcomes vary between individuals. Read more about weight loss treatment at Burst Health.

Frequently Asked Questions

How do I calculate my calorie deficit in Australia?

Estimate what your body uses now from your sex, age, weight and activity, then work out the same figure at a healthy weight for your height. The second figure is your daily target, with nothing further taken off. The difference is your deficit. The calculator above follows the Nutrient Reference Values method and shows the answer in kilojoules and calories.

Is 1,500 calories a day a calorie deficit?

It depends on what your body uses. 1,500 calories is about 6,300 kJ. For an adult who uses the average of about 8,700 kJ a day, that would be a gap of about 2,400 kJ. A tall or very active person uses more, and a smaller or less active person uses less. Use the calculator to compare it with your own estimate.

Is 1,200 calories a day too little for a deficit?

Yes, for most adults. 1,200 calories is about 5,000 kJ, the floor the Better Health Channel gives for a daily intake. Restrictive fad diets can leave you constantly hungry and tired, and short of vitamins and minerals. If a plan takes you below that level, talk to a GP or accredited practising dietitian first.

How big should a calorie deficit be to lose weight?

The Australian Obesity Management Algorithm (2024) puts a modest energy deficit for adults above a healthy weight at about 2,000 to 4,000 kJ (about 480 to 960 calories) a day. Your own gap at a healthy weight may be smaller or larger. No figure can promise a weekly loss, because rates of weight loss vary widely between individuals. Judge progress over several weeks, not one weigh-in.

References

• Eat for Health (NHMRC). Nutrient Reference Values for Australia and New Zealand: Dietary energy. https://www.eatforhealth.gov.au/nutrient-reference-values/nutrients/dietary-energy
• Eat for Health (NHMRC). Daily energy requirements calculator. https://www.eatforhealth.gov.au/nutrition-calculators/daily-energy-requirements-calculator
• FAO, WHO and UNU (2004). Human energy requirements, Chapter 5: Energy requirements of adults (Schofield equations, Table 5.2). https://www.fao.org/4/y5686e/y5686e07.htm
• Markovic TP, et al. The Australian Obesity Management Algorithm: a simple tool to guide the management of obesity in primary care (July 2024). https://www.diabetessociety.com.au/wp-content/uploads/2024/07/Australian-Obesity-Management-Algorithm-July-2024.pdf
• Better Health Channel (Victorian Government). Weight management services. https://www.betterhealth.vic.gov.au/health/HealthyLiving/weight-management-services
• healthdirect. Kilojoules. https://www.healthdirect.gov.au/kilojoules
• healthdirect. Body mass index (BMI) and waist circumference. https://www.healthdirect.gov.au/body-mass-index-bmi-and-waist-circumference
• healthdirect. Weight loss and dieting. https://www.healthdirect.gov.au/weight-loss-and-dieting
• Eat for Health (NHMRC). Australian dietary guidelines 1 to 5. https://www.eatforhealth.gov.au/guidelines/australian-dietary-guidelines-1-5
• Australian Government Department of Health. Physical activity and exercise guidelines for adults (18 to 64 years). https://www.health.gov.au/topics/physical-activity-and-exercise/physical-activity-and-exercise-guidelines-for-all-australians/for-adults-18-to-64-years

This page is general information only and does not replace individual medical advice. Please speak with a registered Australian healthcare practitioner about your own circumstances.