Shift every timestamp in your activity, instantly.

Yes. Drop the FIT into the time adjuster, switch to "Set start to" mode, and choose today's correct time. Every timestamp inside the file - records, laps, sessions, file_id.time_created - shifts by the same offset so the whole activity moves to today consistently. Re-upload to Strava or Garmin Connect and the activity slots into the right day.

Use the offset mode and shift by the timezone delta in hours. If your head unit was set to UTC but you wanted local time (UTC+1 for example), shift by +1 hour. The FIT format stores timestamps as UTC internally - the timezone display is set by the platform reading it - so shifting the underlying timestamp shifts the displayed local time on Strava and Garmin Connect.

Yes - the output is a fully valid FIT re-encoded with the official Garmin SDK, including the correct CRC and file header. Strava treats it like any other upload. If a platform rejects it, the problem is almost always duplicate detection (Strava sees the original at the same start time) rather than file validity. Delete the original first or shift by a larger offset.

No - only fields that store time get shifted. The record stream's lat, lon, altitude, distance, speed, HR, power, cadence, and temperature are untouched. Laps and sessions keep their durations, average values, and totals. Only the absolute timestamps change. Distance and elevation gain numbers are identical before and after the shift.

No - the tool shifts every timestamp in the file together so internal consistency is preserved. A FIT with records timestamped one way and the session timestamped another is malformed and most platforms will reject it. The point of shifting is to keep the activity coherent at a different absolute time.

Use offset mode and shift by hours/minutes. Common scenario: you went for an evening ride but the head unit's GPS-time sync was wrong and the file says 6 AM. Shift by +12 hours (or to the actual start) and the activity moves to the right time of day. Or use exact-new-start mode and type in the correct datetime.

Same underlying timestamp-shifting transform, different UX. The [FIT Clone & Retime](/tools/fit-clone-retime) tool gives you preset "now" and "tomorrow 7am" buttons for the common case of re-staging a benchmark workout. The Time Adjuster gives you full offset controls and an exact-datetime input for trickier cases (timezone fixes, multi-hour shifts, off-by-one-day errors). Use Clone & Retime for fast re-staging; Time Adjuster for surgical timestamp work.

Yes - free, no signup, no upload. The tool exists because most platforms either refuse to let you edit timestamps after upload or charge for the privilege. Drop, shift, download, done.