Short answer: Apple Watch indoor run distance is an estimate. On a treadmill, GPS distance is not available, so Apple Watch relies on motion, calibration, stride, and pace patterns. The treadmill belt distance can be more useful after the workout, especially for pace and split history.
Why indoor run distance can be inaccurate
Outdoor Apple Watch workouts can use GPS. Indoor Run workouts cannot use GPS distance in the same way, because you are running in place relative to the world. Apple Watch estimates distance from wrist motion, sensor data, and previous calibration.
The estimate can drift if your arm swing changes, you hold the treadmill rails, your stride changes with incline, or your recent outdoor calibration does not match your treadmill form.
Common treadmill mismatch cases
- Apple Watch distance is too short: common when arm motion is reduced or stride changes indoors.
- Apple Watch distance is too long: can happen when motion patterns do not match the actual belt pace.
- Kilometers and miles mismatch: double-check the treadmill unit before entering the corrected distance.
- Intervals feel wrong: if the total distance changes, pace and splits need to be recalculated too.
How to correct the saved indoor run
- Finish the workout on Apple Watch as usual.
- Open Fix My Treadmill on iPhone.
- Select the Indoor Run from Apple Health.
- Enter the treadmill distance exactly as shown on the machine.
- Save the corrected copy and review it in Apple Fitness.
What about future workouts?
Apple Watch calibration may improve over time, but treadmill workouts can still vary. If you care about exact treadmill distance, keep using the treadmill display as the source of truth and correct the saved workout when the mismatch matters.
What to review before saving
Before saving a corrected copy, check the treadmill unit, the entered distance, and the workout type. A mile/kilometer mismatch can make pace and weekly totals look wrong even when the correction flow works correctly. If the workout was an Indoor Run, select the Indoor Run from Apple Health. If it was an Indoor Walk, use the walk entry instead.
After entering the treadmill distance, review the corrected pace and splits. Distance-based values change because they depend on the corrected distance and the original workout timing. Heart rate and calories are preserved where HealthKit allows it, rather than being guessed from the new distance.
What happens after correction
The corrected workout is saved as a new Apple Health entry. The original Apple Watch workout is not overwritten. This gives you a chance to open Apple Fitness, compare the result, and delete the inaccurate original only after the corrected copy looks right.
If you leave both entries in place, Apple Fitness can show both workouts and your totals can count both. If your goal is a clean training history, keep the corrected copy and remove the original workout from Apple Fitness after checking it.
More guides
- How to fix wrong Apple Watch treadmill distance
- Can you edit Apple Watch workout distance?
- All guides
Try it: Fix My Treadmill includes 3 free fixes, then offers a one-time unlock for unlimited corrections. Download it on the App Store.