What RMR measures
Resting metabolic rate (RMR) is the energy your body spends doing nothing at all. Fully at rest it still keeps your heart beating, your lungs moving, your temperature steady, and your cells repairing, and that work has a calorie cost. For most people RMR is the largest slice of daily energy use, usually 60 to 75 percent of the total.
Because it is so large, RMR is the natural starting point for a calorie plan. Once you know roughly how much you burn at rest, adding your activity on top gives your full daily burn, and that figure is what you eat around to hold, lose, or gain weight.
RMR versus BMR
RMR and basal metabolic rate (BMR) often get used interchangeably, and for planning they are close enough to treat as one number. The gap is in measurement. A true BMR is taken in a lab after an overnight fast, first thing in the morning, following overnight rest. RMR is measured under gentler conditions, without that strict protocol, so a measured RMR usually reads a few percent above a measured BMR.
The prediction equations here do not know which conditions you will sit under, so they return a single estimate that stands in for both. If you have already used the BMR calculator, you will see the same figure here from the same inputs. The label differs; the math does not.
How this calculator works
The headline number comes from the Mifflin-St Jeor equation, the most reliable predictor for the general population (Mifflin MD, St Jeor ST et al., 1990):
- Men: RMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
- Women: RMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161
For comparison the calculator also shows the revised Harris-Benedict estimate (Harris JA, Benedict FG, 1918; Roza and Shizgal revision, 1984), which tends to read a little higher. If you enter a body fat percentage, the estimate switches to the Katch-McArdle equation, which predicts resting calories from lean body mass rather than total weight, so it fits lean and muscular people better.
What changes your RMR
Two people at the same weight can have different resting rates. The main levers are:
- Muscle mass. Lean tissue burns more at rest than fat, so more muscle lifts RMR.
- Body size. A larger body has more tissue to maintain.
- Age. RMR drifts down over the years, mostly because muscle is lost.
- Sex. Men usually have a higher RMR because they carry more lean mass on average.
A long calorie deficit also nudges RMR down as the body adapts to less food. Resistance training and enough protein are the practical ways to protect it.
From RMR to a daily calorie target
RMR on its own is not what you eat. It is the resting floor. To reach your total daily energy expenditure, multiply RMR by an activity factor, from about 1.2 for a mostly seated day up to 1.9 for hard daily training. The TDEE calculator applies that step and gives the number you burn on a normal day.
From there the goal sets the target. The maintenance calorie calculator shows the intake that holds your weight, and the calorie calculator sets a target for losing or gaining at a chosen rate. RMR is where all of those numbers begin. These are estimates, not medical advice; check with a doctor or dietitian before a large change.
