Formulas and sources
Each formula this calculator uses, where it comes from, and what it leaves out. "How it works" shows the same formula with your own numbers.
BMR, Mifflin-St Jeor equation, men
For men
- BMR
- energy used at rest, in calories a day (the paper calls it resting energy expenditure)
- W
- weight in kg
- H
- height in cm
- A
- age in years
For both equations, Imperial entries are converted first (lb × 0.453592, in × 2.54).
Source: Uses the formula in Mifflin and colleagues (1990) [1]. How it compares with measured resting energy use is in Frankenfield and colleagues (2005) [2]. The conversion factors are NIST's, rounded [3].
BMR, Mifflin-St Jeor equation, women
For women
- BMR
- energy used at rest, in calories a day (the paper calls it resting energy expenditure)
- W
- weight in kg
- H
- height in cm
- A
- age in years
Source: Uses the formula in Mifflin and colleagues (1990) [1], as for men.
Total daily energy expenditure
Every mode
- TDEE
- total daily energy expenditure, in calories a day
- BMR
- from the equation above
- AF
- activity factor: Sedentary 1.2, Light Activity 1.375, Moderate Activity 1.55, Active 1.725, Very Active 1.9
Source: The five activity factors are widely used; no primary source found. Searched: the Harris and Benedict (1918), Mifflin and colleagues (1990) and Roza and Shizgal (1984) papers, the 1989 US Recommended Dietary Allowances, the FAO/WHO/UNU reports of 1985 and 2004, the National Academies' 2023 energy report, PubMed and Europe PMC.
Goal calories, Weight Loss
Weight Loss mode
- Goal Calories
- the daily calories for the goal
- TDEE
- from the formula above
The calculator notes a Weight Loss figure below 1,200 calories a day for women or 1,500 for men, the low ends of the guideline's weight-loss ranges [4]. Under 800 calories it adds the guideline's line that it keeps diets under 800 calories a day for medical settings with supervision.
Source: A 500 calorie daily deficit is one of the options in a 2013 US clinical guideline for adults with overweight or obesity [4].
Goal calories, Weight Gain
Weight Gain mode
- Goal Calories
- the daily calories for the goal
- TDEE
- from the formula above
Source: The 500 calorie surplus: no primary source found. Searched: the 2017 position stand of the International Society of Sports Nutrition on diets and body composition, which gives no surplus figure.
Weeks to your target weight
Weight Loss and Weight Gain modes, with a target weight
- weeks
- weeks to reach the target, rounded
- weight change
- the gap between your weight and the target
- weekly rate
- 0.45 kg a week in Metric, 1 lb a week in Imperial
A 500 calorie daily change is 3,500 calories a week. At 3,500 calories per pound, that is about 1 lb, or 0.45 kg, a week.
Source: Based on the 3,500 calories per pound rule in Wishnofsky (1958) [5], who gave it for weight lost on a high-protein, low-calorie diet and for weight gained as fat. The NHLBI's 1998 report also gives about 1 lb a week for a deficit of 500 calories a day [6]. The rule's limits are in Hall and colleagues (2011) [7].
Macro grams from goal calories
Every mode
- grams
- grams of protein, carbs or fat a day
- goal calories
- the daily calories for the goal
- share
- each goal's split of calories, in percent of protein/carbs/fat: Maintenance 30/40/30, Weight Loss 40/30/30, Weight Gain 30/50/20
- calories per gram
- 4 for protein and carbs, 9 for fat
Grams are rounded to whole numbers. The splits are CalcTrail's own starting splits, not a published standard. Maintenance and Weight Loss put carbohydrate below the adult range of 45% to 65%, and Weight Loss puts protein above 35%.
Source: Uses the general factors of 4, 4 and 9 calories per gram in the FDA's food-labeling rule, 21 CFR 101.9 [8]. The adult ranges are the National Academies' [9].
Calorie cycling
In the Calorie Cycling section
- day calories
- the target for one day, rounded
- day percentage
- that day's share of the goal, from the Zig-Zag, High/Low Days or Custom pattern
Zig-Zag is 110%, 90%, 110%, 90%, 110% and 90% from Monday to Saturday and 100% on Sunday, so the week averages the target. High/Low Days puts the high days first in the week and the low days last, with any days between at 100%. Custom takes 0% to 200% for each day.
Source: CalcTrail's own patterns; no single publisher.
Sources
- Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition, 1990; 51(2): 241-247.
- Frankenfield D, Roth-Yousey L, Compher C. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. Journal of the American Dietetic Association, 2005; 105(5): 775-789.
- National Institute of Standards and Technology. NIST Guide to the SI, Appendix B.9: Factors for units listed by kind of quantity or field of science, length and mass. Special Publication 811.
- Jensen MD, Ryan DH, Apovian CM, et al. 2013 AHA/ACC/TOS guideline for the management of overweight and obesity in adults: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines and The Obesity Society, recommendation 3a, diets for weight loss. Circulation, 2014; 129(25 Suppl 2): S102-S138.
- Wishnofsky M. Caloric equivalents of gained or lost weight, summary, page 546. American Journal of Clinical Nutrition, 1958; 6(5): 542-546.
- National Heart, Lung, and Blood Institute. Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults: The Evidence Report, pages 72 and 74 (pages 104 and 106 of the PDF). NIH Publication No. 98-4083, September 1998.
- Hall KD, Sacks G, Chandramohan D, et al. Quantification of the effect of energy imbalance on bodyweight. The Lancet, 2011; 378(9793): 826-837.
- Food and Drug Administration. 21 CFR 101.9: Nutrition labeling of food, paragraph (c)(1)(i)(B), calories per gram. eCFR, current as of October 1, 2026.
- Institute of Medicine, National Academies Press. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids, Summary, page 15. 2002/2005.
What this calculator does not cover
- The equation was derived from adults aged 19 to 78 [1], but the calculator accepts any age from 1 to 120.
- It has no inputs for pregnancy or breastfeeding, and it does not account for medical conditions or medicines that change energy use.
- The timeline is a straight line. Real change slows: about half of the eventual weight change from a lasting change in intake comes in the first year [7].
- Weight lost is not all fat: in the NHLBI's 1998 evidence report, about a quarter of it is lean tissue [6].
- The equation estimates an average. A 2005 review found notable individual errors, and older adults and US ethnic minorities were underrepresented in the studies [2].
Sources checked on .