How the calculator works out your calories and macros

The four steps

The calculator works in four steps from your details to a daily target in calories, grams and percentages. Each step builds on the previous one.

• Resting energy: what your body uses when you do nothing.
• Maintenance: your resting energy times a factor for how much you move.
• Goal: when losing weight a part comes off, when building muscle a part is added.
• Macros: protein, fat and carbohydrate, converted to grams and percentages.

Step one: your resting energy

Resting energy is the energy your body needs per day to keep functioning: breathing, your heart, your body temperature. The calculator uses the Mifflin and St Jeor formula: 10 times your weight in kilos, plus 6.25 times your height in centimetres, minus 5 times your age in years, plus or minus a fixed value for your sex.

• For a man that fixed value is plus 5.
• For a woman it is minus 161.
• If you choose 'other', the calculator takes the average of the two, because the formula only knows male and female.
• Why this formula: in a comparison with measured resting energy, Mifflin-St Jeor was within ten percent of the measured value for most adults, more often than other common formulas (Frankenfield and colleagues).

At a very high body weight every formula is less accurate.

Step two: your maintenance

Your maintenance is the number of calories at which your weight stays the same. The calculator multiplies your resting energy by a factor that matches how much you move.

• Mostly sitting: factor 1.2.
• Lightly active, exercising a few times a week: 1.375.
• Moderately active, exercising three to five times a week: 1.55.
• Active, exercising six to seven times a week: 1.725.
• Very active, heavy work or intensive daily training: 1.9.

These factors are common multipliers and do not come from a single study. No formula knows how much you really move, and that is the biggest source of error.

Step three: your goal

Then the calculator adjusts your maintenance to your goal, using the middle of the ranges from the article 'Setting a good goal'.

• Losing weight: 17.5 percent off, the middle of fifteen to twenty percent below maintenance.
• Maintenance: nothing is added or taken off.
• Building muscle: 12.5 percent added, the middle of ten to fifteen percent above maintenance.
• The daily target never goes below your resting energy. If the calculated target is lower, the calculator raises it to your resting energy and says so: we do not suggest eating below your resting energy, not even when losing weight.

Why not a bigger deficit: in a study of elite athletes, the group that lost weight more slowly gained muscle and the group that lost weight quickly did not, while both groups lost about the same amount of fat (Garthe and colleagues).

Step four: your macros

The macros follow in a fixed order: protein first, then fat, and carbohydrate is what is left.

• Protein: 2 grams per kilo of body weight, 2.2 grams when losing weight. A meta-analysis of strength training research found that extra protein above about 1.6 grams per kilo added almost nothing to muscle growth (Morton and colleagues); in a deficit a little more can help to hold on to muscle (Helms and colleagues).
• The protein share never goes above 35 percent of your calories, so that carbohydrate is always left at a high body weight.
• Fat: 25 percent of your calories, within the guideline for athletes (Thomas and colleagues).
• Carbohydrate: everything that is left.
• Protein and fat are rounded to whole percentages and carbohydrate is the rest, so the sum is always exactly the whole. The grams follow from that with the same factors as in the app: 4 calories per gram of protein and carbohydrate and 9 per gram of fat.

A worked example

This example is checked against the real calculation: if it is shown here, the calculator arrives at it too.

A man of 80 kg and 180 cm, aged 30, moderately active, who wants to lose weight: resting energy 1,780 kcal, maintenance 2,759 kcal, target 2,276 kcal at 31/44/25 percent, so 176.4 g protein, 250.4 g carbohydrate and 63.2 g fat.

What the result is not

It is an estimate from a formula, not a measurement.

• The real value can be tens of percent off, because nobody knows how much you really move. So eat the way you are used to for a few weeks and look at your own weekly average: that is more accurate.
• The calculator works with a weight from 30 to 300 kilos, a height from 100 to 250 centimetres and an age from 14 to 100 years. Outside that the formula is no longer reliable.
• For young people who are still growing, an estimate like this should be discussed with a doctor or dietitian.

This is general information and not medical advice. If you have a condition, take medication, are pregnant or are recovering from an eating disorder, talk to a doctor or dietitian first.

Sources

These are the sources the calculation rests on. The activity factors have no source of their own: they are common multipliers.

1. Mifflin, M. D., St Jeor, S. T., Hill, L. A., Scott, B. J., Daugherty, S. A., & Koh, Y. O. (1990). A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition, 51(2), 241–247. The formula for resting energy.
2. Frankenfield, D., Roth-Yousey, L., & Compher, C. (2005). Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. Journal of the American Dietetic Association, 105(5), 775–789. jandonline.org Compares the common formulas with measured resting energy.
3. Morton, R. W., Murphy, K. T., McKellar, S. R., et al. (2018). A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. British Journal of Sports Medicine, 52(6), 376–384. How much protein still adds something in strength training.
4. Helms, E. R., Zinn, C., Rowlands, D. S., & Brown, S. R. (2014). A systematic review of dietary protein during caloric restriction in resistance trained lean athletes: a case for higher intakes. International Journal of Sport Nutrition and Exercise Metabolism, 24(2), 127–138. Protein during a deficit in trained athletes.
5. Thomas, D. T., Erdman, K. A., & Burke, L. M. (2016). Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. Journal of the Academy of Nutrition and Dietetics, 116(3), 501–528. Nutrition guidelines for athletes, including fat.
6. Garthe, I., Raastad, T., Refsnes, P. E., Koivisto, A., & Sundgot-Borgen, J. (2011). Effect of two different weight-loss rates on body composition and strength and power-related performance in elite athletes. International Journal of Sport Nutrition and Exercise Metabolism, 21(2), 97–104. The pace of weight loss, muscle mass and strength in elite athletes.

Further

Read where the guidelines come from and what the macros do for your body, or work out your own goal with the calculator on the website.

Setting a sensible goal What macros do for your body Losing weight without losing muscle

Calculate your calories Back to knowledge