How far back can I backfill activities?

Some challenges do NOT allow any backfilling. There is a setting when creating a challenge to turn backfilling on or off. If backfilling is turned on, then a participants previous activities can be backfilled up to 60 days. Third party app activities will be automatically backfilled, up to 60 days. For manual entries, the user can change the date on the activity entry form to go back up to 60 days. 

Challenge Hound restricts unlimited backfilling because it can be disruptive to other participants. For example, if you're in a six month challenge and someone joins five months in, most participants agree that the new participant should not catapult into the leaderboard. In other words, drastic changes to the leaderboard due to backfilling can be frustrating to existing participants. 

To put this another way, imagine you are running a long race. You are one mile or kilometer from the finish line and someone darts out from the woods ahead of you and beats you to the finish line. The person may have actually run the full race, but it is still incredibly disappointing, demotivating, and frustrating. It is way more fun, fair, and engaging to see who you are competing against throughout the race and dash to the finsih line together.