How many calories do you burn at rest? The equation behind your target

By Robert Robinson, founder of Neato Health · September 15, 2026 · 4 min read

Most of the calories you burn in a day are burned doing nothing. Here is how that number is estimated, how wrong the estimate can be, and why Neato treats it as a starting point rather than a fact.

Ask most people how many calories they burn in a day and they think of exercise. But for almost everyone, the largest share of the day’s burn happens with no movement at all: keeping the heart beating, the brain running, the body warm, and the cells repaired. That is resting energy expenditure, and for a typical adult it is 60 to 75 percent of everything they burn. Get it wrong and every number downstream of it — the daily target, the deficit, the date you reach your goal — is wrong by the same amount.

Where the number comes from

Nobody measures your resting burn directly unless you sit in a metabolic chamber or breathe into a calorimeter for an hour. Everyone else uses a prediction equation: a formula that takes what is easy to know about you — sex, height, weight, age — and returns the resting burn of the average person with those measurements.

Neato uses the equation published by Mifflin, St Jeor and colleagues in 1990. They measured resting energy expenditure in 498 healthy adults by indirect calorimetry and fitted a formula to the results:

For a 40-year-old man of 180 cm and 85 kg that gives 1,780 calories a day at rest. For a 40-year-old woman of 165 cm and 70 kg it gives 1,370. The numbers are in calories per day, and they describe a body lying still, awake, in a comfortable room, twelve hours after a meal.

Why this equation and not another

There are older formulas. Harris-Benedict, from 1919, is the one that shows up in most calculators. In 2005, Frankenfield and colleagues reviewed the published comparisons and found that Mifflin-St Jeor predicted resting burn within 10 percent of the measured value more often than any of the alternatives: about 82 percent of non-obese adults and 70 percent of obese adults. Harris-Benedict tended to run high, especially in heavier people, which matters because an overestimate of resting burn turns into an overestimate of how much you can eat.

The American Dietetic Association (now the Academy of Nutrition and Dietetics) adopted Mifflin-St Jeor as its recommended equation on the strength of that review, and it has stayed the default in clinical dietetics since.

How wrong it can be for you

“Within 10 percent for 82 percent of people” is a good record for a formula with four inputs. It is also a promise that one person in five will be off by more than 10 percent, and a few will be off by 20. Two people with identical height, weight, age and sex can differ by 300 calories a day at rest. The equation cannot see the difference, because it cannot see what the weight is made of. Muscle burns more at rest than fat does, so a lean 85 kg man burns more than a soft one, and the formula gives them the same number.

There is a second, slower effect. Leibel, Rosenbaum and Hirsch showed in 1995 that when people lose 10 percent of their body weight, their energy expenditure drops by more than the lost tissue alone would predict — the body becomes more economical as it shrinks. The formula only knows your new weight, not that you got there by dieting, so it will slightly overstate the burn of someone who has recently lost a lot.

What Neato does with it

Neato treats the Mifflin-St Jeor number as the opening estimate, not the verdict. Three things happen to it:

1. It is matched to Apple Health’s definition. Apple reports a Resting Energy figure that includes a small amount of ordinary daytime physiology the lab definition excludes. Neato scales the equation by 1.1 so that its resting number and the one on your Apple Watch describe the same thing and can be compared.
2. Your scale corrects it. Once you have logged food on most days for two weeks and weighed in a few times, Neato has a ledger: what you ate, and what your weight did. If you ate 2,000 a day and held steady, your real burn was about 2,000, whatever the formula said. The estimate walks toward that evidence, slowly enough that a week of water weight cannot fool it. The details are in why the scale jumps around.
3. You can override it. If you have had your resting metabolic rate measured, or you know from experience where your maintenance calories sit, type the number in Goals and the formula steps aside. Clear the field and it comes back.

What it is not

Resting burn is not the number of calories you can eat. It is the floor. The rest of the day’s burn — walking, chores, workouts, and even digesting food — is added on top, which is a separate estimate with its own guide: move calories versus workout calories. The two together are your daily burn, and the daily target is that burn minus whatever deficit your goal calls for.

A last practical note. Because the equation is linear in weight, it moves about 10 calories per kilogram, or roughly 4.5 calories per pound. Losing 20 pounds lowers your resting burn by about 90 calories a day. That is why a target that worked in month one is a little too generous by month four, and why Neato recomputes it from your latest weight rather than the one you started with.

Neato’s guides are general wellness information built from the published research cited above. They are not a diagnosis, treatment, or medical advice, and they don’t know your history. For decisions about your health, talk to your doctor.