Your rating changes after every game. So, in effect, all your games in a particular format count towards your rating. Your Ratings Deviation/RD (an indication of how accurate your rating is) will impact how wide rating swings are.
Once you have played a lot of games, your RD will decrease so that rating swings are mild. Or if you play someone with a high RD, you rating change will likely be less.
Here is a FAQ on ratings and at the end is link that goes into more detail: https://support.chess.com/customer/portal/articles/1444777-how-do-ratings-work-
What is the length of time /number of games that chess.com uses for your rating? eg rating based on last 30 games or all games in the last month.