The end date of a season is always a bit elusive because it tends to get delayed or change as we get deeper into it. This has been the case quite often, particularly with Chapter 2: Season 2 which experienced quite a few delays due to the various situations going on in the world. Hopefully, Epic will have a handle on Season 4 and not have to delay it quite as often.
Chapter 2: Season 3 End Date
The end date for Season 3 is currently thought to happen on September 14th, 2020. This is based off of leaked information found by VastBlast on Twitter. These details are found via the Fortnite API, so they are from Epic themselves. The date that is displayed on Fortnite's official Battle Pass page and listed in the battle pass in game, however, is list as August 26th, 2020. That seems pretty unlikely, especially because a lot of updates have already been delayed, and Epic has been pretty notorious for delaying things at least by a few weeks or more in recent seasons.
Additions to the Battle Pass
When we get close to the end, we'll usually get some added challenges that yield rewards. For a long time, there were overtime challenges, which gave you an opportunity to earn some more styles for your battle pass skins. Season 2, however, did not include these for whatever reason. We got some additional challenges, but we didn't get more styles for the skins. We'll have to wait and see how Epic handles it in Season 3, and whether or not they experience delays!
That's everything we know right now about the end of Season 3! We'll be updating this post whenever there's news about the date shifting, or if some particular news of note shows up that will likely cause delays.