FIT file won't upload: how to fix it
Strava says the file is corrupted, that it has corrupted time data, or just "There was an error processing your activity." Garmin Connect says the file is invalid or corrupt. The activity is on the device, so the data exists, but the platform won't take it. Most of the time the file is fixable in a couple of minutes.
Why a FIT file gets rejected
A FIT file has a header, a stream of messages, and a checksum at the end. If the device died before it finished writing, the end is missing. If a sync was interrupted, the middle can be damaged. Either way the checksum doesn't match and the platform gives up rather than guess.
Less often the file is fine but isn't an activity. Devices also write FIT files for settings, sleep, daily monitoring, and courses, and those upload nowhere.
Step 1: get the file off the device
Use the copy on the device rather than one that already went through a failed sync. Plug it in and look in the activity folder (Garmin/Activity on a Garmin). On a watch that syncs by phone only, export the original from Garmin Connect if the activity appears there, or from the brand's app.
Step 2: open it in the editor
Drag the file onto FIT File Editor, or start from the repair page. There are three things that can happen.
It opens normally. The file was readable after all. Export a fresh copy anyway: the editor writes a clean file with a new checksum, and that alone often gets past the upload error.
"Recovered most of this file. The rest was unreadable." The file was truncated or damaged partway. The editor kept every complete record it could read and dropped the broken tail. Check the map and the stats. Then export. You get a valid file with the totals recalculated from the data that survived.
"This is a FIT file, but not an activity recording." It is a settings, monitoring, or course file. There is no activity to upload. Look for a different file with the right timestamp.
Step 3: upload the exported file
Delete any failed or partial upload of the same activity first, so the platform doesn't see a duplicate, then upload the exported file.
If it still won't open
- Corrupted time data. Strava gives this message when the date jumps forward partway through the file, sometimes by years. This editor can shift a whole activity's time, but it doesn't fix a jump in the middle yet. Strava's own help points to the Corrupt Time Fixer on FIT File Tools for this one.
- A second opinion. GOTOES repairs corrupted FIT files for free from its FIT file viewer and its merge tool, using a different method, so it can succeed where this editor's recovery doesn't.
- Nothing readable at all. If the file is a few hundred bytes, the recording never really started. There is nothing to recover.
- Deeply corrupted. The paid Fit File Repair Tool on Windows goes further than any web tool. It is the last resort. The tools comparison has the details.
Preventing it next time
Most truncated files come from a dead battery or a hard reset with an activity still recording. Save the activity before the battery gets low, and if the device freezes, let it come back up on its own before pulling the power. That gives it a chance to close the file properly.