Short answer
Resting energy is roughly what your body would use over 24 hours doing nothing at all. The Mifflin-St Jeor equation estimates it as (10 × kg) + (6.25 × cm) - (5 × age), then +5 on the male version or -161 on the female version.
The number that comes out is an estimate from a population equation, not a measurement of you. That is the part worth holding on to, and it is why this page runs two equations instead of one.
BMR, RMR and REE are not quite the same thing
These get used interchangeably online, which is where a lot of the confusion starts. RMR and REE are the same thing under two names: resting metabolic rate and resting energy expenditure. BMR, basal metabolic rate, is the stricter one.
The difference is the measurement conditions rather than the biology. A true BMR measurement is taken after an overnight fast, immediately on waking, following at least eight hours of sleep in the test facility. An RMR or REE measurement only asks you to rest quietly beforehand, usually for 15 to 30 minutes. Because the conditions are looser, measured RMR tends to come out around 10% above measured BMR.
There is a detail here that most calculators labelled "BMR" quietly skip. Mifflin-St Jeor was published as a resting energy equation, not a basal one, so what it predicts is closer to REE than to strict laboratory BMR. That is why this page labels its output resting energy. In practice, for planning a food log, the distinction changes very little; it matters mostly when you are comparing a calculator against a clinic measurement and wondering why they differ.
The two equations on this page
Mifflin-St Jeor is the one most dietetics guidance reaches for now. The revised Harris-Benedict equation, updated by Roza and Shizgal in 1984 from the 1919 original, is the other figure you will still see widely quoted.
| Equation | Male version | Female version |
|---|---|---|
| Mifflin-St Jeor | (10 × kg) + (6.25 × cm) - (5 × age) + 5 | (10 × kg) + (6.25 × cm) - (5 × age) - 161 |
| Revised Harris-Benedict | 88.362 + (13.397 × kg) + (4.799 × cm) - (5.677 × age) | 447.593 + (9.247 × kg) + (3.098 × cm) - (4.330 × age) |
Both were built on a two-version, sex-specific structure from their source studies. A formula fitted to a study population cannot describe every body, and if you are unsure which version is appropriate for you, that is a question for a clinician rather than a dropdown.
Why the two numbers disagree
They were fitted to different groups of people. The revised Harris-Benedict coefficients came from 337 adults, 168 men and 169 women. Mifflin-St Jeor came from a different sample and was designed to predict resting energy expenditure specifically.
The gap the calculator shows you is the useful part. It is not telling you which equation is right. It is showing you the width of the uncertainty around a number people usually quote to the nearest calorie. If the two equations land 150 Calories apart for your body, then no single figure in that range deserves to be treated as exact.
Resting energy is not a calorie target
This is the one thing on the page worth being blunt about. Resting energy covers your body at rest and nothing else. It excludes walking, standing, work, chores, and every form of training. Eating at that number is not a moderate plan; it is eating as though you spent the day unconscious.
Deliberately eating at or below estimated resting energy is a pattern that belongs under the supervision of a clinician or registered dietitian, not one to adopt from a web calculator. If you want an intake figure, the number you want is maintenance, which starts from resting energy and adds an allowance for how you actually move.
What to do with the number
Treat it as the first of two steps. The TDEE calculator takes resting energy and applies an activity assumption to estimate maintenance, and it shows the nearby activity range so one dropdown choice does not read as a measurement. The maintenance calories guide explains how much weight that estimate deserves.
After 14 to 28 days of complete logs and comparable weigh-ins, the TDEE from weight change calculator works out the maintenance your own data implies, which is a better answer than any equation on this page. The equations are where you start when you have no log yet.
Limits
Prediction equations do not account for body composition, thyroid or other medical conditions, medication, pregnancy, injury, or the demands of serious training. Research on athletes has found that standard resting-metabolic-rate equations can be insufficient for that population. Indirect calorimetry is the actual measurement; everything here is an estimate standing in for one.
This tool is general information for adults. It is not for children, pregnancy, breastfeeding, eating-disorder treatment, chronic disease, or setting a medically necessary intake. Speak with a qualified clinician or registered dietitian for personal guidance, and stop tracking if it causes distress, guilt, or compulsive checking.
The revised Harris-Benedict coefficients come from Roza and Shizgal's 1984 reevaluation. The BMR and RMR measurement-condition distinction follows ACE's summary of the two protocols. On the limits of prediction equations in trained populations, see this study of resting metabolic rate equations in young adult national-team athletes. NIDDK's Body Weight Planner covers why adult calorie needs shift over time.