# Calorie Calculator: BMR and Daily Calories by the Mifflin-St Jeor Equation

Page: https://hirantha.me/tools/calorie-calculator
Part of: Hirantha Sandaruwan Lakshan free tools (https://hirantha.me/tools)
Updated: 2026-10-13

Estimate the calories you use each day from age, sex, height, weight and activity, with the Mifflin-St Jeor working shown and a rough range, not a prescription.

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Enter your age, sex, weight, height and activity level to estimate the calories your body uses in a day: first at rest (BMR, basal metabolic rate), then with an activity multiplier (TDEE, total daily energy expenditure). The equation and the working are shown, the revised Harris-Benedict equation sits beside it for comparison, and the answer is a range, not a prescription. A weekly weight change you choose is turned into what it implies for daily intake, with a floor below which no figure is shown. This is general information, not medical advice.

Resting energy comes from the Mifflin-St Jeor equation, published in 1990 from indirect calorimetry on 498 healthy adults aged 19 to 78. The simplified form in the abstract is 10 x weight in kg + 6.25 x height in cm - 5 x age in years, then + 5 for men or - 161 for women. The abstract also prints the unrounded version, 9.99 x weight + 6.25 x height - 4.92 x age + 166 x sex (male 1, female 0) - 161, which lands within a few calories of the simplified one. A 2005 systematic review in the Journal of the American Dietetic Association found Mifflin-St Jeor the equation most likely to predict resting energy to within 10% of measured, while noting that noteworthy errors still occur for individuals.

The revised Harris-Benedict equation (Roza and Shizgal, 1984) is, for men, 88.362 + 13.397 x kg + 4.799 x cm - 5.677 x age, and for women 447.593 + 9.247 x kg + 3.098 x cm - 4.330 x age. Roza and Shizgal reported that it predicts resting energy in normally nourished people to a precision of about 14%, and the Mifflin authors found the original 1919 equations overestimated measured values by 5% in their sample. The tool shows the other equation's result next to your chosen one so you can see how far apart they land.

Daily energy use is the resting figure times an activity multiplier: 1.2 sedentary, 1.375 lightly active, 1.55 moderately active, 1.725 very active and 1.9 extra active. These five numbers are a widely used convention. We could not trace them to a primary publication, so treat them as a rough way to describe a typical week, not a measurement. The FAO, WHO and UNU 2001 report uses a different scheme, physical activity levels of 1.40 to 1.69 for sedentary or light activity lifestyles, 1.70 to 1.99 for active or moderately active ones and 2.00 to 2.40 for vigorous ones, and notes that values above 2.40 are difficult to maintain over a long period. The tool shows a rough range of 10% either way, the margin Mifflin-St Jeor is more likely than other equations to stay within for resting energy. The activity multiplier adds more uncertainty than that.

A weekly weight change is turned into calories with the old rule of about 7,700 kcal per kilogram (3,500 kcal per pound), so 0.5 kg a week is about 550 kcal a day. This is a rough rule. Kevin Hall of the US National Institutes of Health showed in 2008 that the energy needed per unit of weight lost depends on how much body fat a person starts with, and that the rule overestimates the deficit needed for people with less body fat. A 2011 Lancet paper he co-authored modelled that body weight responds slowly to a change in intake, with a half time of about a year. So the figures here are arithmetic, not a forecast, and no result is promised.

For a loss scenario the tool never shows an intake below 1,200 kcal a day for women or 1,500 kcal a day for men. Those are the lower ends of the weight-loss levels in an American Family Physician patient handout (women 1,200 to 1,500, men 1,500 to 1,800). Other guidance starts some supervised plans lower: the US NHLBI booklet describes plans of 1,000 to 1,200 kcal for most women and 1,200 to 1,600 for men, and says very low calorie diets of under 800 calories a day need special monitoring by a doctor, and the NIH Body Weight Planner will not accept less than 1,000 kcal a day. The higher floors are the cautious choice here. The tool also stops at 0.9 kg (2 lb) a week, the top of the 1 to 2 lb a week the NHLBI booklet links to a deficit of 500 to 1,000 calories a day. It shows no weight-loss figure at all when your weight and height give a BMI below 18.5.

Activity multipliers used here (a common convention, not a measurement), with an example for a resting energy of 1,600 kcal:
| Activity level | Multiplier | Typical week | Example daily energy |
| --- | --- | --- | --- |
| Sedentary | 1.2 | Little or no exercise, mostly sitting | 1,920 kcal |
| Lightly active | 1.375 | Light exercise or sport 1 to 3 days a week | 2,200 kcal |
| Moderately active | 1.55 | Moderate exercise or sport 3 to 5 days a week | 2,480 kcal |
| Very active | 1.725 | Hard exercise or sport 6 to 7 days a week | 2,760 kcal |
| Extra active | 1.9 | Very hard exercise most days or a physical job | 3,040 kcal |

Q: How many calories do I need a day?
A: It depends on your age, sex, size and activity. The NHS says an average man needs about 2,500 kcal a day and an average woman about 2,000 kcal, and that your own figure could be different. This calculator estimates a figure from your own numbers, as a range. It is general information, so ask a doctor or dietitian about what is right for you.

Q: What is the difference between BMR and TDEE?
A: BMR is the energy the body uses at rest. TDEE is your total daily energy use, which adds everything you do in a day on top of that. This tool estimates BMR with an equation and then multiplies it by an activity level to get the TDEE figure, the calories that would roughly keep your weight the same.

Q: Which is better, Mifflin-St Jeor or Harris-Benedict?
A: In the 2005 systematic review in the Journal of the American Dietetic Association, Mifflin-St Jeor predicted resting energy to within 10% of measured in more people than the other common equations, and had the narrowest error range. The review still warned of noteworthy errors for individuals, and found older adults and some ethnic groups underrepresented in the studies. Neither is exact, which is why both are shown.

Q: Are the activity multipliers 1.2 to 1.9 official?
A: No. They are a widely used convention, and we could not trace them to a primary publication. The FAO, WHO and UNU 2001 report describes activity as a physical activity level (1.40 to 1.69 sedentary or light, 1.70 to 1.99 active or moderately active, 2.00 to 2.40 vigorous). Pick the level that fits a typical week and treat the result as a starting estimate.

Q: How many calories are in a kilogram of body weight?
A: The old rule says about 7,700 kcal per kilogram (3,500 per pound), which this tool uses to turn a weekly change into a daily calorie gap. It is a rough rule. Research from the US National Institutes of Health shows the energy needed depends on a person's body fat, that it overestimates the deficit for people with less body fat, and that the body adapts over time. Do not expect weight to change in a straight line.

Q: What is the lowest number of calories I should eat?
A: There is no single figure for everyone. For a loss scenario this tool will not show an intake below 1,200 kcal a day for women or 1,500 kcal a day for men, the lower ends of the weight-loss levels in an American Family Physician handout. The NHLBI says very low calorie diets of under 800 calories a day should not be used routinely because they need special monitoring by a doctor. It also shows no weight-loss figure when your weight and height give a BMI below 18.5. Ask a doctor or dietitian before eating much less than your estimated needs.

Q: Does this work in pregnancy, while breastfeeding, for under 18s or for older adults?
A: Not for pregnancy, breastfeeding or under 18s. Needs are different, so ask a doctor or dietitian. The Mifflin-St Jeor equation was built from adults aged 19 to 78 and the review above found older adults underrepresented, so outside that age range the estimate is less reliable, and the tool says so.

Q: Should I eat exactly the number this calculator gives?
A: No. It is an estimate with a margin of error of at least 10%, based on groups of people and a guessed activity level. It is not a prescription. If you track what you eat and your weight for a few weeks, you learn more about your own needs than any equation can tell you, and a doctor or dietitian can help you interpret it.

Sources: Mifflin MD et al., A new predictive equation for resting energy expenditure in healthy individuals, Am J Clin Nutr 1990 (abstract with both forms of the equation), checked 2026-10-13 (https://pubmed.ncbi.nlm.nih.gov/2305711/); Roza AM and Shizgal HM, The Harris Benedict equation reevaluated, Am J Clin Nutr 1984 (abstract: precision of 14%), checked 2026-10-13 (https://pubmed.ncbi.nlm.nih.gov/6741850/); Pavlidou E et al., Revised Harris-Benedict Equation: New Human Resting Metabolic Rate Equation, Metabolites 2023 (table of the 1984 coefficients), checked 2026-10-13 (https://pmc.ncbi.nlm.nih.gov/articles/PMC9967803/); Frankenfield D et al., Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review, J Am Diet Assoc 2005, checked 2026-10-13 (https://pubmed.ncbi.nlm.nih.gov/15883556/); Hall KD, What is the required energy deficit per unit weight loss?, Int J Obes 2008, checked 2026-10-13 (https://pubmed.ncbi.nlm.nih.gov/17848938/); Hall KD et al., Quantification of the effect of energy imbalance on bodyweight, Lancet 2011, checked 2026-10-13 (https://pubmed.ncbi.nlm.nih.gov/21872751/); NHLBI, Aim for a Healthy Weight, NIH Publication 05-5213 (calorie levels, 1 to 2 lb a week, very low calorie diets), checked 2026-10-13 (https://www.nhlbi.nih.gov/sites/default/files/publications/05-5213.pdf); American Family Physician, Weight Loss: Practical Tips (patient handout, 2016: 1,200 to 1,500 kcal for women, 1,500 to 1,800 for men), checked 2026-10-13 (https://www.aafp.org/pubs/afp/issues/2016/0901/p361-s1.html); NIDDK, Body Weight Planner (minimum 1,000 kcal a day), checked 2026-10-13 (https://www.niddk.nih.gov/bwp); FAO, Human energy requirements: report of a Joint FAO/WHO/UNU Expert Consultation, 2001 (Table 5.3, physical activity levels), checked 2026-10-13 (https://www.fao.org/3/y5686e/y5686e07.htm); NHS, Understanding calories (average daily needs), checked 2026-10-13 (https://www.nhs.uk/live-well/healthy-weight/managing-your-weight/understanding-calories/)

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