How many calories do you burn a day?
Your body and your steps set a range. Four weeks of weigh-ins find your number inside it.
How it works
Your resting burn comes from Mifflin-St Jeor (1990). The range is that number give or take 10%: in a 2013 test on 337 adults, Mifflin-St Jeor came within 10% of a lab measurement for 82% of them. The revised Harris-Benedict, and Katch-McArdle and Cunningham when you add bodyfat, are the ticks.
Your steps pick the level that multiplies it. In the US Dietary Guidelines' calorie tables, moderately active means walking about 1.5 to 3 miles a day on top of daily life. At about 2,000 steps a mile, that's 3,000 to 6,000 extra steps on a day that would be under 5,000 without them. So the levels follow the step bands from pedometer research:
| Steps a day | Level | Times resting |
|---|---|---|
| Under 5,000 | Sedentary | 1.2 |
| 5,000 to 7,499 | Lightly active | 1.375 |
| 7,500 to 9,999 | Moderately active | 1.55 |
| 10,000 to 12,499 | Active | 1.725 |
| 12,500 and up | Very active | 1.9 |
One level up adds 10 to 15%, more than the formulas disagree by. That's why steps beat a word you pick.
Training your steps don't count, like lifting or cycling, is added at its own cost: its METs minus one (resting is already counted), times your weight in kilos, times the hours, from the Compendium of Physical Activities. An hour of lifting at 80 kg is about 200 calories. Runs and walks are in your steps already.
Your watch's number lands on the bar. Across 56 studies, the Apple Watch's calorie estimate was off by about 28% on average, against about 4% for heart rate. Use it to compare one day with another, not to set your maintenance.
9 sources
- Mifflin MD, St Jeor ST, et al. A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition, 1990pubmed.ncbi.nlm.nih.gov
- Roza AM, Shizgal HM. The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass. American Journal of Clinical Nutrition, 1984.
- Cunningham JJ. A reanalysis of the factors influencing basal metabolic rate in normal adults. American Journal of Clinical Nutrition, 1980.
- Katch FI, McArdle WD. Nutrition, Weight Control, and Exercise. 1983.
- Frankenfield DC. Bias and accuracy of resting metabolic rate equations in non-obese and obese adults. Clinical Nutrition, 2013pubmed.ncbi.nlm.nih.gov
- Tudor-Locke C, Bassett DR. How many steps/day are enough? Preliminary pedometer indices for public health. Sports Medicine, 2004pubmed.ncbi.nlm.nih.gov
- US Department of Agriculture and US Department of Health and Human Services. Dietary Guidelines for Americans, 2020 to 2025, estimated calorie needsdietaryguidelines.gov
- Ainsworth BE, Haskell WL, Herrmann SD, et al. 2011 Compendium of Physical Activities: a second update of codes and MET values. Medicine and Science in Sports and Exercise, 2011.
- Choe and Kang. A pooled analysis of 56 Apple Watch studies: error for energy expenditure, heart rate and steps. Physiological Measurement, 2025.
