Large discrepency in distance and pace of Apple Watch Ultra three indoor treadmill running and the actual treadmill distance and pace since update to iOS 27

Since updated iOS 27 I have noticed a significant difference in the distance and pace recorded on my watch when running on an indoor treadmill and the actual treadmill pace and distance which I know is accurate. This has only been since updating my watch and I used to find the watch was incredibly accurate to match the treadmill speed. I am almost 1-2km less on my watch than I am on the treadmill for example if I do a 15 km run at 10km/hr set on the treadmill this is obviously 6mins/km and takes me 90 mins but my watch is saying I’ve only ran 13km at around a 6min30 pace. Any updates to fix this issue?

Posted on Oct 26, 2026 3:39 AM

1 reply

WheelieNick

Level 9 (74,110 points)

Oct 28, 2026 5:05 AM in response to DrMim

The distance and pace discrepancy on your Apple Watch Ultra is a known issue caused by a new step-and-distance estimation algorithm introduced in watchOS 27.

What Causes the Issue?

New Algorithm: Apple changed how the internal accelerometer and motion sensors calculate indoor movement, which has drastically skewed indoor treadmill readings for many users (making distances shorter or paces significantly slower than actual).
Not Fixed Yet by Minor Updates: Minor patch updates like watchOS 27.0.1 have not resolved the core calculation bug for most affected users.

Potential Workarounds & Fixes

Recalibrate Your Watch: You can try outdoor calibration to help the watch relearn your stride length.
- Make sure Location Services and Motion Calibration & Distance are enabled under iPhone Settings > Privacy & Security.
- Go to an open outdoor area with good GPS and do an outdoor walk or run for at least 20 minutes.
- You can also reset your existing fitness calibration data (iPhone Watch app > My Watch > Privacy > Reset Fitness Calibration Data) before doing an outdoor session.