Calories burned by exercise: an honest table

Your watch says that 30-minute run torched 500 calories, so you reward yourself with a snack that's exactly 500 calories, and wonder why nothing changes. The problem: fitness trackers routinely overestimate calorie burn, often by 20 to 40 percent. Here are honest numbers, calculated the way exercise scientists do, and the reason the real figure is lower than you hope.

How this is calculated

Every activity has a MET value, a measure of how many times your resting energy use it demands, drawn from the Compendium of Physical Activities, the reference researchers use.¹ The formula is simple: calories per minute = MET × 3.5 × your weight in kg ÷ 200. Crucially, burn scales with bodyweight, which is why a heavier person burns more doing the same activity. The table shows calories for 30 minutes at three bodyweights.

Estimates from standard MET values; individual burn varies with fitness, intensity and efficiency.

Why your tracker says more

Two reasons. First, wrist trackers estimate from heart rate and movement, both of which are noisy, and manufacturers tend to err high because a bigger number feels motivating. Second, most trackers report your total calories during exercise, including the ones you'd have burned anyway just being alive. If your run burned 350 calories but you'd have burned 40 sitting on the sofa, the run only "cost" you an extra 310. The gap is small per session and large over a month of eating it all back.

The lesson: you can't out-train the fork

Look at the table honestly. A hard 30-minute run for a 75 kg person is under 400 calories, roughly one chocolate bar and a banana. This is why exercise alone is a slow way to lose fat: it's simply easier to not eat calories than to burn them. A single restaurant dessert can undo an hour of cardio.

This isn't an argument against exercise, it's an argument for what exercise is actually for. Train for strength and muscle (which protects your metabolism), for health, and for fitness. Let your diet do the heavy lifting on the calorie deficit, and let daily walking, which barely raises hunger, top up the burn.²

Using the numbers well

The afterburn is smaller than you've heard

Fitness marketing loves "afterburn", the extra calories you keep burning after a workout, technically called EPOC. It's real, but modest: for most sessions it adds a small percentage to the total, not the hundreds of bonus calories often implied. Intense intervals and heavy lifting produce a bit more afterburn than steady cardio, but not enough to change the picture in the table. Don't choose a workout for its afterburn; choose it because you'll do it consistently and it builds strength or fitness you value.

Where exercise really helps a diet

If the direct calorie burn is modest, why exercise at all for fat loss? Two reasons that don't show up in the table. Resistance training signals your body to keep muscle while you diet, so more of the weight you lose is fat, and muscle keeps your metabolism higher. And daily movement, especially walking, adds up over the whole day without triggering the hunger that hard cardio can. The workouts in the table burn less than your tracker claims, but paired with a real calorie deficit they protect your results and your health in ways calories burned alone can't measure.

Cardio machines lie too

It's not just wrist trackers. The calorie readout on treadmills, cross-trainers and bikes is generally optimistic, and worse, most don't ask your weight, so they can't be accurate for you specifically. A lighter person burns less than the machine's default assumes; a heavier person may burn a little more. Treat any machine's calorie number as a rough, usually inflated, estimate rather than a figure to eat back. If you want a realistic number, the MET table above, matched to your actual bodyweight, beats the console every time.

If you want to account for exercise, use these conservative figures rather than your tracker's, and eat back at most half of what you burn to leave a margin for error. Better still, set your calorie target with your activity already built in and don't eat back exercise at all, so any workout is a bonus to your deficit. Exercise is one of the best things you can do for your body. Just don't ask it to be your whole diet, because the maths won't cooperate.