How to change the date or time of a Strava activity

The ride was this morning, but Strava says it started at 3 a.m., or last year, or in 2004. Strava has no field for the date or start time of a recorded activity: its help page says the only way to fix the timestamps on an existing activity is to upload it again. So the fix is to change the time in the file itself, then replace the activity.

Why the time is wrong

The device's clock was wrong. A watch or bike computer that lost its settings can stamp the whole activity with the wrong date or year.
An indoor workout with no GPS. With no position in the file, Strava uses the time zone in your profile. If that was wrong when you uploaded, the activity sits hours off.
A year in the 2000s. If you recorded with the Strava app, Strava's help ties this to a GPS rollover.
Two days in one activity. If the activity's elapsed time is huge, the device recorded on two different days. That's a cut, not a time shift: see delete part of a Strava activity.

For an indoor workout, fix the time zone in your Strava profile first, so the next upload lands right.

Step 1: get the original file

From Strava: open the activity on the website, click the three-dot menu, and choose Export Original.
From Garmin Connect: open the activity, click the gear icon, and choose Export Original. You get a .zip; the editor opens it directly.
From the device: plug it in and look in Garmin/Activity (or your device's activity folder) for the .fit file from that day.

Step 2: set the right start time

Open the file in FIT File Editor. Drag it onto the page or press browse.
Click the details button next to the file name (the sliders icon).
Set Start date & time to when the activity really started. The field shows your computer's time zone.
Press Export and save the new file.

Every timestamp in the file moves by the same amount: each record, lap, and the summary. The activity keeps its length, distance, and all its data, just at the new time. The file is read and written in your browser; nothing is uploaded.

Step 3: replace the activity on Strava

Delete the original activity first, then upload the new file at strava.com/upload. If you upload first, Strava sees two activities at the same time and rejects the new one as a duplicate.

Deleting the activity removes its kudos, comments, and photos. Save any photos you want to keep before you delete it. The duplicate activity guide covers the order that works on each platform.

Worth knowing

Shift whole hours for a time zone mistake. If the activity is exactly some hours off, move it by that many hours and keep the minutes.
Change the date before merging. Two recordings that need to sit apart in time, or line up, can be shifted first and then merged.
Garmin Connect reads the same file. Upload the fixed file there too, and every app the file goes to shows the right date.

For the tool on its own, see Change the date and time of a FIT file.