What Your BMR Covers

Your body uses energy in three main ways each day (Better Health Channel):

• Basal metabolic rate: the energy needed at rest for breathing, keeping the heart beating, growing and repairing cells and adjusting hormone levels. It is the largest part of daily energy use, 50 to 80% of it.
• Digesting food: about 5 to 10% of daily energy use goes on digesting, absorbing and storing what you eat and drink.
• Physical activity: about 20% for a moderately active person, and the only part of energy use you have any control over.

Your BMR is largely set by your lean mass, especially muscle, because lean tissue needs a lot of energy to keep going. Anything that reduces lean mass lowers your BMR.

How the Calculator Works

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

1. It estimates your BMR from your sex, age and weight with the Schofield equations. These equations use weight, not height, so the calculator does not ask for your height.
2. Each sex has one equation for 19 to 30 years, one for 31 to 50 and one for over 70. For ages 51 to 70, it averages the 31 to 50 and over 70 results, as the Nutrient Reference Values do.
3. It multiplies your BMR by the activity factor for each type of day in the table below, which gives a range of energy used a day for each level.

The calculator rounds kilojoules to the nearest 100 and calories to the nearest 10. It converts at 4.184 kJ per calorie (kilocalorie). Some Australian sources round this to 4.18 or 4.2, so their figures can differ by a few calories.

Activity Levels

The activity factors come from Table 4 of the Nutrient Reference Values. Pick the row that sounds most like a usual day for you.

The table leaves out the lowest level (1.2), which applies to people who are confined to a bed or chair.

A Worked Example

Take a woman aged 45 who weighs 79 kg and works at a desk:

• BMR: 0.034 x 79 + 3.538 = 6.224 MJ, or about 6,200 kJ (about 1,480 calories) a day
• mostly seated (1.4 to 1.5): about 8,700 to 9,300 kJ (about 2,080 to 2,220 calories) a day
• sport 4 to 5 times a week would add about 1,900 kJ (about 450 calories) a day

Her seated range starts at healthdirect's figure for what an average adult needs, about 8,700 kJ a day. Her real use could be higher or lower than the estimate.

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 BMR in older people.
• A measured BMR is better than a predicted one where it is available, and choosing an activity level is a judgement call.
• Hormones affect metabolism too. An underactive thyroid, for example, slows it. If you have unexplained weight changes, talk to a GP.
• 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

Because lean mass drives your BMR, the Better Health Channel suggests combining exercise, particularly weight-bearing and resistance exercise to build muscle, with healthier eating patterns rather than diet changes alone. Eating too few kilojoules encourages the body to slow its metabolism to save energy. People also tend to lose muscle as they age, and strength and resistance training can reduce or prevent that loss.

A healthy diet is 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 daily energy into protein, carbohydrate and fat, see macros for weight loss.

Australia's physical activity 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 ideas, see how many steps a day to lose weight and how to lose weight: a realistic guide.

Using Your Numbers for a Weight Goal

Your daily total, not your BMR, is the figure to compare with what you eat and drink. To turn it into a target, see what a calorie deficit is and how to work out yours and how many calories a day to lose weight. As weight comes down, the energy your body uses comes down too, which is one reason weight loss can slow down over time.

When to Get Personal Advice

Talk to a GP or accredited practising dietitian before you change how much you eat if you have a health condition, or if you are unsure which numbers apply to you. 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

What is a normal BMR?

There is no single normal figure. Your BMR depends on your sex, age and weight, and largely on how much lean mass, such as muscle, you carry. With the equations on this page, a 60-year-old woman weighing 70 kg has an estimated BMR of about 5,700 kJ (1,360 calories), and a 25-year-old man weighing 100 kg about 9,200 kJ (2,200 calories). A higher or lower number is not a score.

What is a good BMR for my age?

No BMR is better or worse for a given age. The equations change at 30, 50 and 70 years, and after 50 the estimate for the same weight is usually lower. People tend to lose muscle as they age, probably more from being less active than from ageing itself, and strength and resistance training can reduce or prevent that loss. Enter your own age above to see your estimate.

How many calories do I use a day if my BMR is 1,500?

Multiply your BMR by your activity factor. A BMR of 1,500 calories (about 6,300 kJ) comes to about 2,100 to 2,250 calories a day with mostly seated work (factor 1.4 to 1.5), and about 3,000 to 3,600 calories with heavy physical work (2.0 to 2.4). These are estimates only, and real energy use varies between individuals.

Should I eat at my BMR to lose weight?

Not as a general rule. Your BMR is the energy you use at rest, so it leaves out what you use to move and to digest food. Eating too few kilojoules encourages the body to slow its metabolism, and a good weight management service advises against intakes below 5,000 kJ (1,200 calories) a day. A GP or accredited practising dietitian can help you set a target that suits you.

How do I calculate my BMR?

Put your sex, age and weight into the Schofield equations used by Australia's Nutrient Reference Values. For example, a woman aged 31 to 50 multiplies her weight in kilograms by 0.034 and adds 3.538, which gives megajoules a day. Multiply that by 1,000 for kilojoules, then divide by 4.184 for calories. The calculator above does this for every age band.

References

• Better Health Channel (Victorian Government). Metabolism.
• Eat for Health (NHMRC). Nutrient Reference Values for Australia and New Zealand: Dietary energy.
• FAO, WHO and UNU (2004). Human energy requirements, Chapter 5: Energy requirements of adults (Schofield equations, Table 5.2).
• FAO, WHO and UNU (2004). Human energy requirements, Introduction (1 kcal = 4.184 kJ).
• healthdirect. Kilojoules.
• Better Health Channel (Victorian Government). Weight management services.
• Eat for Health (NHMRC). Australian dietary guidelines 1 to 5.
• Australian Government Department of Health. Physical activity and exercise guidelines 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.