Calorie calculator: maintenance, bulking and cutting

Step 1: resting energy expenditure

The calculator first estimates what your body burns at rest with the Mifflin-St Jeor equation, published in 1990 from measurements on 498 adults:

• Men: 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5
• Women: 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161

A systematic review published in 2005 in the Journal of the American Dietetic Association compared the four most widely used equations: Mifflin-St Jeor was the most reliable, estimating within 10% of the measured value for the largest number of people. It remains an estimate: the authors note individual errors, and older adults were underrepresented in validation studies.

Step 2: activity level

Resting expenditure is then multiplied by a physical activity level (PAL), taken from the FAO, WHO and United Nations University report on human energy requirements:

• Light activity: PAL of 1.40 to 1.69
• Moderate activity: PAL of 1.70 to 1.99
• High activity: PAL of 2.00 to 2.40

The calculator uses the middle of each range and also shows both ends. The report gives a useful benchmark: one hour of moderate to vigorous exercise every day raises the PAL of a person with a desk job from about 1.55 to 1.75. Three or four lifting sessions a week with an office job are therefore closer to light than to moderate activity.

Step 3: your goal

Bulking. The review by Iraki and colleagues (2019) on off-season nutrition for bodybuilders recommends a surplus of about 10 to 20%, for a gain of 0.25 to 0.5% of body weight per week in novice and intermediate lifters. Advanced lifters should be more conservative.

Cutting. Helms and colleagues (2014) recommend setting calorie intake to lose about 0.5 to 1% of body weight per week, to best preserve muscle.

Why no number for cutting

Turning weight loss into calories requires knowing how much energy a lost kilo contains. The common rule of 7,700 kcal per kilo (3,500 kcal per pound) only holds for people with a lot of body fat: Kevin Hall (2008) showed that it overestimates the deficit needed in leaner people, who also lose some lean mass, which holds less energy. Rather than display a falsely precise number, the calculator gives the rate to aim for: your scale, used under the same conditions each week, will tell you whether to adjust.

To work out how much protein to eat, use our protein calculator.

These estimates apply to healthy adults. If you are pregnant, have an eating disorder or a medical condition, ask a doctor or a registered dietitian.

Sources

• Mifflin M.D. et al., "A new predictive equation for resting energy expenditure in healthy individuals", American Journal of Clinical Nutrition, 1990.
• Frankenfield D. et al., "Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review", Journal of the American Dietetic Association, 2005.
• FAO, WHO, UNU, "Human energy requirements: Report of a Joint FAO/WHO/UNU Expert Consultation", FAO Food and Nutrition Technical Report Series 1, 2004.
• Iraki J. et al., "Nutrition Recommendations for Bodybuilders in the Off-Season: A Narrative Review", Sports, 2019.
• Helms E.R. et al., "Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation", Journal of the International Society of Sports Nutrition, 2014.
• Hall K.D., "What is the required energy deficit per unit weight loss?", International Journal of Obesity, 2008.