Guides for editing lap data in .fit files

ButterLaps is a browser tool for editing the lap boundaries in a .fit activity file – merge an accidental split, move a late lap press, or re-cut a run into the segments you want, without altering anything else your device recorded. Nothing is uploaded; your file never leaves your device.

Open ButterLaps → Already know the fix? Skip the guides and edit your file now.

Or read on – the guides below walk through the common fixes, device by device.

• Garmin Connect has no lap editor – here's what to do instead

  Garmin Connect shows your lap table but won't let you change it. Here's how to fix accidental, late, or autolap splits without touching anything else in your file.

• Merge away an accidental lap press on Garmin

  Bumped the lap button mid-effort? A phantom split turns one clean rep into two ragged halves. Here's how to merge it away in two minutes.

• Nudge interval and track-workout laps into place

  Structured workouts that deviated from the plan, or late presses at the end of each rep – fix the boundaries so your splits match what you actually ran.

• Recut your laps when the workout went off-plan

  A stale template, an added rep, a step that ended while you were still running – the watch slices the file by the plan, not the run. Re-cut the laps to what you actually ran, step names intact.

• Reslice your Garmin run any way you want

  Your watch auto-lapped every kilometre, but you want 5 km blocks, climb segments, or an exact lap distance or duration. Load the file, place your own boundaries, download the result.

• Correct Stryd lap splits without losing data

  The run that started this project, re-edited and compared in Runalyze – and the rules ButterLaps edits by: untouched laps stay byte-identical, and every recalculated number is checked against your device's own totals.

• Edit Apple Watch workout laps

  Apple Fitness has no lap editor. Export your workout as a .fit via HealthFit or WorkOutDoors, drop it into ButterLaps, and fix the splits on your phone.