How many calories does exercise really burn?

Exercise burns calories, but the numbers on the treadmill display or fitness watch are often inaccurate. Understanding what drives calorie burn during exercise helps you set realistic expectations and avoid the frustration of working hard without seeing results.

What determines calorie burn during exercise

Your body weight is the single biggest factor. A 200-pound person burns roughly 30 percent more calories than a 150-pound person doing the same activity at the same intensity. Heavier people move more mass, so the energy cost is higher.

Exercise intensity matters just as much. Doubling your running speed from 5 mph to 10 mph more than doubles your calorie burn per minute, because air resistance increases and efficiency decreases at higher speeds.

Duration is the third variable. Thirty minutes of moderate cycling burns fewer total calories than 60 minutes, but the per-minute rate may be similar. For weight loss, total calorie burn matters more than intensity.

Calorie burn by activity

Walking at a moderate pace of 3 mph burns roughly 250 to 350 calories per hour for a 155-pound person. Brisk walking at 4 mph increases that to 300 to 400 calories per hour.

Running at 6 mph (10-minute-mile pace) burns about 600 to 750 calories per hour for the same person. At 8 mph (7.5-minute-mile pace), that rises to 800 to 1,000 calories per hour.

Cycling at a moderate 12 to 14 mph burns 450 to 550 calories per hour. At a vigorous pace of 16 to 19 mph, that jumps to 650 to 800 calories per hour.

Swimming laps at a moderate pace burns 400 to 500 calories per hour. The resistance of water makes swimming highly efficient for calorie burn, though skill level significantly affects the actual number.

Strength training burns 200 to 400 calories per hour during the workout itself, but the afterburn effect (excess post-exercise oxygen consumption, or EPOC) adds 50 to 100 additional calories over the next several hours as your body repairs muscle tissue.

Why fitness trackers overestimate

Most wrist-based trackers overestimate calorie burn by 20 to 50 percent. They use heart rate and movement data to estimate, but they cannot account for individual differences in metabolism, muscle mass, and exercise efficiency. Studies consistently show that no consumer device is reliably accurate for calorie tracking.

The most accurate method is using MET (metabolic equivalent of task) values combined with your body weight. Each activity has a known MET value. For running at 6 mph, the MET value is about 9.8. Multiply by your weight in kilograms and the duration in hours to get a reasonable estimate.

Practical takeaways

Do not eat back all the calories your tracker says you burned. A good rule is to eat back half at most if you are trying to lose weight. The margin of error is simply too large to trust the full number.

Focus on consistency rather than precision. A 300-calorie run every day adds up to 2,100 calories per week, which translates to about 0.6 pounds of fat loss per week. The exact number matters less than the habit. Use the Calories Burned Calculator to get a science-based estimate for any activity and build your exercise plan around sustainable effort.