Work out how many calories you need a day to keep, lose or gain weight, using the 2023 National Academies equations, and see where that energy goes.
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The formulas use different numbers for female and male bodies.
In years. For adults 19 and over.
Pick the one closest to a normal day. If you're between two, pick the lower one.
Used when you lose or gain weight.
Enter your details to see your result.
The default formula comes from the US National Academies' 2023 Dietary Reference Intakes for Energy1. Its equations are fitted to daily energy use measured with doubly labelled water, the most accurate method outside a lab, in people of every body size. Each sex and activity level has its own equation, with height in cm and weight in kg:
The other two Formula options start from resting energy and multiply it by 1.4, 1.6, 1.75 or 2.05, the typical activity ratio the same report gives for each level1:
The bar splits the total three ways. Resting comes from Mifflin-St Jeor (or Katch-McArdle). Digesting food is 10%, the middle of the 5 to 15% measured on mixed diets5. Moving is what's left.
Pace sets a weekly change of 0.25, 0.5 or 1% of your body weight when losing, and 0.125, 0.25 or 0.5% when gaining. Those steps follow sports nutrition reviews that aim to keep muscle during loss and limit fat during gain67. Each kilogram counts as 7,700 kcal, so the daily change is weekly kg × 7,700 ÷ 7.
A daily cut stops at 1,000 kcal and a surplus at 500. The target never goes below 1,200 kcal for women or 1,500 for men; that floor is a common rule of thumb rather than a clinical standard. Below a BMI of 18.5 the calculator won't set a weight-loss target at all.
People who match on every input still burn different amounts. For the default equations the standard error is 241 kcal a day for women and 342 for men1, and the range on your result shows that spread. The other two formulas show ±10%.
The report's advice is to start at the estimate, watch your weight over a few weeks and adjust1. Expect change to slow down as well. Your body uses less energy as it gets lighter, and a lasting change in eating takes about a year to show half its effect8. Read the weekly pace as a starting rate.
Other calculators often come out lower because they multiply resting energy by 1.2 for a desk-based day. The FAO, WHO and UN University put sedentary and light lifestyles at 1.40 to 1.69 times basal energy use9.
Activity is the hardest input to judge, and the report says no reliable tool exists to place one person in a level1. If you're between two, pick the lower one.
Warning
This is for adults aged 19 and over. It doesn't cover pregnancy or breastfeeding, which need extra energy1.
National Academies of Sciences, Engineering, and Medicine (2023). Dietary Reference Intakes for Energy. National Academies Press. ↩ ↩2 ↩3 ↩4 ↩5 ↩6
Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO (1990). A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition 51(2):241-247. ↩
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. ↩
Cunningham JJ (1991). Body composition as a determinant of energy expenditure: a synthetic review and a proposed general prediction equation. American Journal of Clinical Nutrition 54(6):963-969. ↩
Westerterp KR (2004). Diet induced thermogenesis. Nutrition & Metabolism 1:5. ↩
Helms ER, Aragon AA, Fitschen PJ (2014). Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation. Journal of the International Society of Sports Nutrition 11:20. ↩
Iraki J, Fitschen P, Espinar S, Helms E (2019). Nutrition recommendations for bodybuilders in the off-season: a narrative review. Sports 7(7):154. ↩
Hall KD, Sacks G, Chandramohan D, et al. (2011). Quantification of the effect of energy imbalance on bodyweight. The Lancet 378(9793):826-837. ↩
FAO, WHO, UNU (2004). Human energy requirements: report of a joint FAO/WHO/UNU expert consultation. FAO Food and Nutrition Technical Report Series 1. ↩