TDEE Calculator: Maintenance Calories From Mifflin-St Jeor
- Calculator
- About 3 min
- Mifflin-St Jeor 1990 with Harris-Benedict activity factors
- Runs in your browser, nothing is sent
- Medical review: Medical review pending
What this calculator works out
Total daily energy expenditure, or TDEE, is the energy you burn in a whole day: resting metabolism, digestion, planned exercise and everything else you do while upright. The calculator estimates the resting part from a published equation and scales it by an activity factor you choose, so you can see both pieces and judge the weaker one.
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Maintenance calories (TDEE)
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Resting energy expenditure
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The activity factor applied
How this compares with a typical online quiz
| Feature | Typical free quiz | Regenerated.com |
|---|---|---|
| Equation named | Sometimes | Mifflin-St Jeor 1990, with the activity factors after Harris and Benedict |
| Activity factor shown with the result | Rarely | Yes, as its own output |
| Deficit and surplus math explained | A single goal number | The arithmetic, the floor, and why the 3,500 kcal rule overstates loss |
| Body-fat alternative covered | Mixed into one result | Katch-McArdle explained in prose, with a worked number, on the BMR page |
| Limits of the equation stated | No | Yes: within 10 percent of measured in about 7 to 8 adults out of 10 |
| Email required for the result | Often | Never |
| Answers sent to a server | Often | Never; scored in your browser, counts-only events |
Turning maintenance into a deficit or surplus
A deficit is simply your TDEE minus a chosen amount. Take the worked example of a man with a TDEE of 2,759 kcal: a 500 kcal deficit gives 2,259 kcal per day, and a 20 percent deficit gives about 2,207. For a surplus, 250 to 500 kcal above maintenance (3,009 to 3,259 kcal in the example) is the range most strength coaches use because larger surpluses add more fat than muscle. The old rule that 3,500 kcal equals one pound of fat predicts about a pound a week from a 500 kcal deficit, but it overstates what actually happens: the body's needs fall as weight falls, and the loss slows. Hall and colleagues' 2011 model in The Lancet puts it more realistically, with roughly half of the eventual weight change arriving in the first year.
The floor matters as much as the target. A deficit that lands below your resting energy expenditure, or below about 1,200 kcal for most women and 1,500 kcal for most men, leaves little room for protein, fiber and micronutrients and is the territory of medically supervised programs, not a self-directed plan. In the example of a woman with a resting rate of 1,320 kcal and a light-activity TDEE of 1,815 kcal, a 500 kcal cut would put her at 1,315 kcal, essentially her resting rate. A 300 kcal deficit, or a 300 kcal deficit plus more daily movement, is the more sustainable arithmetic.
Whatever target you pick, recalculate every 5 kg (about 10 lb) of change, because TDEE moves with body weight. A loss of 10 kg typically lowers the Mifflin-St Jeor resting estimate by 100 kcal and the TDEE by 120 to 190 kcal depending on the activity factor, so the deficit that worked in month one is smaller by month four.
Why the activity factor is the weakest link
The resting equation has been tested against indirect calorimetry in hundreds of adults. The activity multipliers have not had that kind of scrutiny; they are rounded conventions carried forward from early twentieth-century metabolism work and applied by dietitians because they are practical. Most people also rate themselves higher than their step counts and training logs would support, and the gap between 1.375 and 1.55 is 12 percent of your whole result. When in doubt, choose the lower factor and let two weeks of weigh-ins correct you.
There is also a biological reason the factors overshoot at the top end. Doubly labeled water studies, which measure energy expenditure directly over a week or two, show that total expenditure does not keep climbing in proportion to activity: very active people burn more than sedentary people, but the curve flattens, a pattern Pontzer and colleagues described in 2016 as constrained energy expenditure. A result above 3,000 kcal is worth checking against a food log and a scale before you eat to it.
Age changes the picture less than most calculators imply. The 2021 life-course study in Science, which pooled doubly labeled water data from more than 6,400 people, found that expenditure adjusted for body composition is essentially stable from the twenties to about 60, then declines by around 0.7 percent a year. Much of the fall people notice in midlife is lost muscle and reduced movement, both of which can be addressed.
TDEE on GLP-1 medication and other weight-loss treatment
Readers on semaglutide or tirzepatide often find they eat well below their calculated TDEE without effort, because the medication reduces appetite. The calculator still has a job here: it shows the resting floor your intake should not sit under for long, and it gives a starting point for protein, which clinicians generally set as grams per kilogram of body weight rather than as a share of a shrinking intake. The trials of both medications measured a fall in lean mass alongside fat, which is why clinic programs pair the prescription with adequate protein and resistance training. The calculator does not set a dose and does not judge whether treatment is appropriate; it gives the energy arithmetic that sits around that decision.
Metabolic adaptation is real but smaller than the headlines. After large losses, measured resting expenditure can sit a few hundred kcal below what the equation predicts for the new weight, an effect documented years after weight loss in the Fothergill study of television contestants. For most people the practical answer is to recalculate at the new weight, assume the equation may overestimate by 5 to 10 percent, and let scale trends settle the rest.
Methodology and sources
The resting part of the result is the Mifflin-St Jeor equation, published in 1990 from indirect calorimetry measurements in about 500 healthy adults aged 19 to 78, both normal weight and obese, in Nevada. Resting energy expenditure in kcal per day equals 10 times weight in kg, plus 6.25 times height in cm, minus 5 times age in years, plus 5 for men or minus 161 for women. In the 2005 systematic review by Frankenfield, Roth-Yousey and Compher it predicted measured resting metabolic rate within 10 percent in 82 percent of non-obese and 70 percent of obese adults, the best record of the equations reviewed, which is why the Academy of Nutrition and Dietetics favors it. Its limits: it was derived in adults, not children or athletes with unusual lean mass; it performs less well at very high body weights; and a single estimate can still miss an individual's measured rate by 200 kcal or more.
The daily total multiplies that resting figure by an activity factor: 1.2 sedentary, 1.375 lightly active, 1.55 moderately active, 1.725 very active, 1.9 extra active. These factors trace to Harris and Benedict's 1919 Carnegie Institution monograph and have been carried through dietetic practice since. Worked example: a man of 80 kg and 180 cm aged 30 has a resting estimate of 800 + 1,125 - 150 + 5 = 1,780 kcal per day; with moderate activity, 1,780 x 1.55 = 2,759 kcal per day. A woman of 65 kg and 165 cm aged 40 has 650 + 1,031 - 200 - 161 = 1,320 kcal at rest and, lightly active, 1,320 x 1.375 = 1,815 kcal per day.
There are no clinical thresholds for TDEE; the bands on the result page are orientation only and describe what a number in that range usually implies for planning. If you know your body-fat percentage, the Katch-McArdle equation (370 + 21.6 x lean mass in kg) is an alternative resting estimate that ignores sex and age; the same 80 kg man at 20 percent body fat has 64 kg of lean mass and a Katch-McArdle resting rate of 1,752 kcal. It is explained with worked numbers on the BMR calculator page but is not computed here, because the two equations should not be mixed in one result.
Medical review: Medical review pending. Last updated .
References
- Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241-247. doi:10.1093/ajcn/51.2.241
- 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. doi:10.1016/j.jada.2005.02.005
- Harris JA, Benedict FG. A Biometric Study of Basal Metabolism in Man. Washington, DC: Carnegie Institution of Washington; 1919. Publication 279.
- Hall KD, Sacks G, Chandramohan D, Chow CC, Wang YC, Gortmaker SL, Swinburn BA. Quantification of the effect of energy imbalance on bodyweight. Lancet. 2011;378(9793):826-837. doi:10.1016/S0140-6736(11)60812-X
- Pontzer H, Yamada Y, Sagayama H, et al. Daily energy expenditure through the human life course. Science. 2021;373(6556):808-812. doi:10.1126/science.abe5017