Every cardio machine lies to you, and the calorie readout is the most creative part. The honest way to estimate what you burned takes about fifteen seconds of arithmetic and one number: the MET value of what you did.
A MET is a multiple of resting metabolism, and one MET is roughly 1 kcal per kilogram of body weight per hour. So the formula is: METs times your weight in kilograms times hours. That is it.
the numbers, from the actual source
MET values come from the Compendium of Physical Activities, a research reference maintained since 1993 and updated most recently in 2024. Some published values from the Compendium:
| Activity | METs | Per hour, 150 lb / 68 kg woman |
|---|---|---|
| Walking, 3.5 mph, level | 4.3 | ~292 cal |
| Stationary bike, general | 7.0 | ~476 cal |
| Running, 6 mph (10 min/mile) | 9.8 | ~666 cal |
| Swimming laps, moderate | 5.8 | ~394 cal |
| Elliptical, moderate | 5.0 | ~340 cal |
A 68 kg woman running 10-minute miles for an hour burns in the neighborhood of 666 calories gross. Subtract what she would have burned sitting on the couch for that hour, roughly 68 calories, and the net cost of the run is closer to 600.
That gross-versus-net distinction is where most calorie math goes wrong, and it matters most for low intensity work. Walking for an hour at 292 calories gross is really about 224 net. The difference is small in absolute terms and large as a proportion.
METs are averages and you are not average
The Compendium values were derived from groups of subjects and assume a resting metabolic rate of 3.5 ml of oxygen per kg per minute. Real resting rates vary. Body composition shifts the number too, because a MET scaled to total body weight overestimates expenditure in someone carrying more fat mass and underestimates it in someone lean and muscular. Running economy varies between individuals by a meaningful margin at the same pace.
So treat any MET estimate as plus or minus 15 to 20 percent. That is still dramatically better than the treadmill console, which usually does not know your weight and always rounds in the flattering direction.
the afterburn is real and small
Excess post-exercise oxygen consumption, EPOC, is the elevated metabolic rate after you stop. It exists. It has been measured. The marketing version, where a 20-minute interval session keeps you burning for 36 hours at some dramatic rate, is not what the measurements show.
Research on EPOC puts the added expenditure at roughly 6 to 15 percent of the calories burned during the exercise itself. On that 666-calorie run, that is 40 to 100 extra calories. Worth having. Not worth restructuring your training around, and definitely not worth the claim that intervals burn more than steady state overall when you account for the fact that you cannot do intervals for an hour.
High intensity work does earn its place, and the case for it is time. If you have 20 minutes, intervals will get you more cardiovascular adaptation and more total expenditure than 20 minutes of easy jogging. If you have an hour, steady state will burn more calories than 20 minutes of intervals plus 40 minutes of recovery, which is what actually happens in practice.
why the scale does not reflect the math
Here is the part that frustrates people, and it is the best-documented finding in the field. Weight loss from exercise interventions is consistently smaller than the arithmetic predicts.
Thomas and colleagues examined this in a 2012 analysis in Obesity Reviews, reviewing exercise trials against predicted losses. The gap comes from several places at once: people eat more without noticing, they move less during the rest of the day, and resting expenditure adjusts downward somewhat. Add in the fact that an hour of running costs 600 calories while a muffin and a latte deliver 700 in eight minutes, and the mechanism is not mysterious.
That is not an argument against cardio. It is an argument against using cardio as your primary calorie-deficit tool. The health returns on aerobic exercise, on blood pressure, insulin sensitivity, resting heart rate and mortality risk, are substantial and almost entirely independent of whether the scale moves.
the dose that the guidelines actually specify
The Physical Activity Guidelines for Americans call for 150 to 300 minutes a week of moderate intensity aerobic activity, or 75 to 150 minutes of vigorous, or a combination, plus muscle-strengthening work on two or more days.
Moderate means you can talk but not sing. Vigorous means you can manage a few words at a time. That talk test is more reliable for most people than a heart rate zone calculated from the 220-minus-age formula, which has a standard deviation of about 10 to 12 beats per minute and can therefore be off by 20 beats in either direction for any given individual.
picking the modality
The MET table makes running look like the obvious winner, and per minute it is. Per week it often is not, because running is the modality people quit. Impact accumulates, and a runner who develops shin pain in week three burns zero calories in week four.
Cycling and swimming produce lower per-minute numbers and far higher adherence in people whose joints complain. Rowing sits in a useful middle: 7 METs at moderate effort, full body, low impact, and brutally boring, which is its own adherence problem.
The cardio that works is the one you will still be doing in March. If you hate the elliptical, its 5 METs are theoretical.