What Exercise Actually Burns: A Reference on Energy Cost

An hour of moderate exercise is commonly 300–500 kcal for a typical adult. That figure is not a target; it is a midpoint from a range that depends on body mass, intensity, and the equation used to estimate it. The number people most often overestimate is the calories burned during exercise, and the overestimate is large enough to explain why many calculated deficits fail to exist. This page derives the figure from the equations that produce it, names the sources, and gives the band rather than the midpoint.

The equations behind the number

Exercise energy expenditure is estimated from the metabolic equivalent of task (MET), a ratio of working metabolic rate to resting metabolic rate. One MET is approximately 1 kcal per kilogram of body mass per hour, a simplification that holds for a 70 kg adult at rest and drifts for other masses. The Compendium of Physical Activities assigns MET values to specific activities; the 2011 edition is the current reference. The arithmetic is:

kilocalories = MET × body mass (kg) × duration (hours)

Example: 70 kg adult, walking at 3.5 mph (4.0 METs), 60 minutes
kcal = 4.0 × 70 × 1.0 = 280 kcal

That 280 kcal is the gross figure. It includes the calories that would have been burned at rest during that hour. The net figure, which is the amount added by the activity, subtracts roughly 1 MET:

net kcal = (MET − 1) × body mass (kg) × duration (hours)
net kcal = (4.0 − 1) × 70 × 1.0 = 210 kcal

The distinction matters because resting metabolic rate does not stop during exercise. For a 70 kg adult, one hour of rest costs about 70 kcal. Reporting the gross figure as if it were the added burn overstates the effect by that amount.

A table by activity and body mass

MET values below are from the 2011 Compendium of Physical Activities. The kilocalorie figures are gross, calculated as MET × mass × 1 hour. The condition column shows the rule set or version that changes the figure.

Two conditions in that table are frequently ignored. First, the equation is linear in body mass, so a 100 kg adult burns roughly 67% more than a 60 kg adult for the same activity. Second, the 2011 Compendium revised many values from the 2000 edition; a figure copied from an older source may differ by 10–15%.

Why machine and watch readouts run high

Exercise machines and wrist-worn devices estimate calories burned from heart rate, acceleration, or a fixed equation. A 2017 study in the Journal of Personalized Medicine compared the Apple Watch, Fitbit Charge HR, and others against indirect calorimetry and found errors ranging from roughly 10% to over 40%, with most devices overestimating. A 2018 study in the Journal of Sports Sciences found similar results for the Apple Watch and Fitbit. The error is not random; it tends in one direction. A reasonable working assumption is that a machine or watch readout is 20–30% above the measured figure for steady-state aerobic exercise, and the error is larger at lower intensities and for activities the device was not calibrated on.

The mechanism is straightforward. Heart rate rises with heat, stress, caffeine, and adrenaline, not only with oxygen consumption. A device that equates heart rate with energy expenditure will attribute those rises to calories burned. Acceleration-based devices miss the energy cost of carrying a load, walking uphill, or cycling against resistance.

Compensation: the part of the burn that does not arrive

A training session does not add its full gross cost to daily expenditure. Two responses erode it. The first is increased intake. A 2009 review by King and colleagues in the International Journal of Obesity found that exercise interventions often produce less weight loss than the calculated energy deficit predicts, and that compensatory eating is one explanation. The second is reduced spontaneous movement. A 2016 study by Pontzer and colleagues in Current Biology found that Hadza hunter-gatherers expended similar total daily energy to sedentary Westerners despite much higher physical activity, suggesting that the body downregulates other activity or metabolic processes. The effect is debated in magnitude, but the direction is consistent: the net addition to daily expenditure is smaller than the gross exercise figure.

A practical band: for a 70 kg adult doing 300 kcal of gross exercise, the net addition to daily expenditure may be 150–250 kcal after accounting for resting metabolism, compensation, and device error. That is one modest meal, not a licence for a larger one.

The deficit that does not exist

A common pattern is to add exercise calories to a calculated maintenance figure and eat them back. If maintenance is estimated at 2,300 kcal by the Mifflin-St Jeor equation, and a watch reports 500 kcal burned, the person eats 2,800 kcal. The watch figure may be 20–30% high, so the true gross burn is 350–400 kcal. Subtracting resting metabolism for that hour (about 70 kcal) gives a net of 280–330 kcal. If compensation reduces spontaneous movement by 50–100 kcal, the net addition is 180–280 kcal. Eating back 500 kcal creates a surplus of 220–320 kcal, not a deficit.

Mifflin-St Jeor itself carries a standard error of roughly 10% for estimating resting metabolic rate in adults. For a calculated maintenance of 2,300 kcal, the band is approximately 2,070–2,530 kcal. Adding an uncertain exercise figure to an uncertain maintenance figure compounds the error.

What people get wrong, and why the mistake is natural

The mistake is treating the exercise readout as a measurement rather than an estimate. It is natural because the device presents a precise number, often to the calorie, and because the figure appears on the same screen as the time and heart rate, which are measured. The precision implies accuracy that the underlying equation does not support. A second natural error is comparing the gross exercise figure to a food label. A 300 kcal exercise session and a 300 kcal snack are not equivalent in the energy balance because the exercise figure includes resting metabolism and the snack figure does not include the energy cost of digesting it, which is roughly 5–10% of intake for mixed meals.

A third error is assuming the burn is constant over a diet. As body mass falls, the energy cost of the same activity falls with it, because the equation is linear in kilograms. A 100 kg adult who loses 20 kg will burn roughly 20% fewer calories for the same walk. Maintenance also falls as mass falls, for the same reason. A deficit that was 500 kcal at the start may be 300 kcal after 10 kg of loss, even if intake and activity are unchanged.

Worked example: a 10 kg loss over six months

This example models the change in maintenance and exercise cost as mass falls. It uses Mifflin-St Jeor for resting metabolic rate and a MET-based estimate for exercise. It is arithmetic, not a prescription.

Starting point: 90 kg adult, moderately active
Mifflin-St Jeor (male): RMR = 10 × 90 + 6.25 × 175 − 5 × 40 + 5 = 1,799 kcal
Activity factor 1.55: maintenance = 1,799 × 1.55 = 2,788 kcal

Exercise: 60 min walking at 3.5 mph (4.0 METs)
Gross = 4.0 × 90 × 1.0 = 360 kcal
Net of resting = (4.0 − 1) × 90 × 1.0 = 270 kcal

After 10 kg loss: 80 kg
RMR = 10 × 80 + 6.25 × 175 − 5 × 40 + 5 = 1,699 kcal
Maintenance = 1,699 × 1.55 = 2,633 kcal

Same walk at 80 kg:
Gross = 4.0 × 80 × 1.0 = 320 kcal
Net = (4.0 − 1) × 80 × 1.0 = 240 kcal

Change in maintenance: 2,788 − 2,633 = 155 kcal
Change in net exercise cost: 270 − 240 = 30 kcal
Total reduction in expenditure for the same day: 185 kcal

A deficit of 500 kcal at 90 kg becomes roughly 315 kcal at 80 kg if intake and activity are unchanged. This is why weight loss slows even when behaviour does not.

The figure to carry

For a typical adult, an hour of moderate exercise is 300–500 kcal gross, 200–400 kcal net of resting metabolism, and less than that after compensation. Machine and watch readouts are commonly 20–30% high. The Compendium of Physical Activities (2011) is the source for MET values; Mifflin-St Jeor is the source for resting metabolic rate, with a standard error near 10%. Any figure that does not name its equation or range is not usable for planning.

This page is for information only and is not medical advice. If you are concerned about your relationship with food or exercise, or if you are restricting intake or overexercising, contact a healthcare provider. In the United States, the National Eating Disorders Association helpline is available at 1-800-931-2237. In the UK, Beat’s helpline is 0808 801 0677.

Frequently asked questions

How many calories does exercise burn? For a 70 kg adult, an hour of moderate exercise is roughly 300–500 kcal gross, calculated as MET × body mass in kilograms × hours. The Compendium of Physical Activities provides the MET values. Net of resting metabolism, subtract about 1 MET, which is roughly 70 kcal for that adult.

Are calories burned walking the same as calories burned running? No. Running at 6 mph is about 9.8 METs, while walking at 3.5 mph is about 4.0 METs, so running burns roughly 2.5 times as much per hour for the same person. The ratio holds across body masses because the equation is linear in kilograms.

Why does my watch say I burned more than the machine? Wrist-worn devices estimate from heart rate and acceleration, and studies have found errors of 10–40%, usually overestimating. Machines use fixed equations that may not match your body mass or the activity. Neither is a measurement of oxygen consumption, which is the reference method.

How many calories burned per day come from exercise? For most adults, planned exercise adds 100–400 kcal to daily expenditure after accounting for resting metabolism and compensation. Total daily expenditure is dominated by resting metabolic rate, which is roughly 60–70% of the total, and by spontaneous movement, not by exercise sessions.

Do exercise calories count toward a deficit? They can, but the net addition is smaller than the gross figure. Compensation through increased intake and reduced spontaneous movement erodes part of the burn, and device error inflates it. Using a band of 50–70% of the readout as the net addition is a more conservative planning figure.