Win % different to what ingame stats say

I am wondering, my W/L ratio in game is way higher than then Win % that is shown on the site, is it because the game doesn’t count late joins as losses while the site does? The loss count on the site is the same as in game though so I’m guessing the W/L is based off all the matches in match history. Is it possible to include a late join count or separate W/L for that as well if that’s the case, as the amount of games I’ve joined late on is too high.