The research behind each step
Every constant on this page comes from published work rather than convention.
- 1.Mifflin MD, St Jeor ST, et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241–247. Read the paper ↗
- 2.Frankenfield D, Roth-Yousey L, Compher C. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. J Am Diet Assoc. 2005;105(5):775–789. Read the paper ↗
- 3.Institute of Medicine. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. Washington DC: National Academies Press; 2005. Read the paper ↗
- 4.Hall KD, Kahan S. Maintenance of lost weight and long-term management of obesity. Med Clin North Am. 2018;102(1):183–197. Read the paper ↗
- 5.Morton RW, et al. A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength. Br J Sports Med. 2018;52(6):376–384. Read the paper ↗
- 6.Bauer J, et al. Evidence-based recommendations for optimal dietary protein intake in older people: a position paper from the PROT-AGE Study Group. J Am Med Dir Assoc. 2013;14(8):542–559. Read the paper ↗
- 7.Estruch R, et al. Primary prevention of cardiovascular disease with a Mediterranean diet supplemented with extra-virgin olive oil or nuts. N Engl J Med. 2018;378(25):e34. Read the paper ↗
- 8.Reynolds A, et al. Carbohydrate quality and human health: a series of systematic reviews and meta-analyses. Lancet. 2019;393(10170):434–445. Read the paper ↗
How accurate is this?
Mifflin-St Jeor is the best-validated equation of its kind, and it is still an estimate: for any individual it typically lands within about 10% of measured resting metabolism, and it can be further out for people at the extremes of body composition. Treat the number as a starting point to adjust from, not a verdict. If your weight is not moving as expected after two or three weeks of consistent eating, change the calorie target rather than assuming the equation was right and you were wrong.
Common questions
Why does this ask for biological sex rather than gender?
The Mifflin-St Jeor equation uses a constant derived from average differences in lean body mass, which tracks with sex assigned at birth rather than gender identity. Choosing "prefer not to say" averages the two constants, which shifts the estimate by roughly 80 kcal.
Why is my protein target higher than the RDA?
The 0.8 g/kg RDA is the amount needed to prevent deficiency, not the amount that best supports lean mass, satiety or healthy ageing. This calculator starts at 1.2 g/kg and rises to 1.6–1.8 g/kg when you are in a deficit or training hard, and to at least 1.4 g/kg over 60, where preserving muscle matters more.
Does the calculator store anything I enter?
Your height, weight and age never leave your browser — the maths runs locally and no account is needed. We do record which goal and eating style were chosen, plus a rough calorie range, to see which options people use.
How often should I recalculate?
Whenever your weight changes by more than a few kilograms, or your training load changes meaningfully. Energy needs move with body mass, so a target set at a much heavier or lighter weight drifts out of date.
This calculator provides general nutrition information, not medical or dietetic advice. It is not appropriate for children, for pregnancy or breastfeeding, or for anyone managing a clinical condition or eating disorder — those situations need individual guidance from a qualified professional.