when do i have to make my bracket by

You usually have to make your March Madness bracket before the first game of the main tournament tips off (the Round of 64), and once that first game starts, brackets lock and you can’t change them. Most major sites follow this rule:

• Official NCAA bracket games: open after Selection Sunday and close at tipoff of the first men’s or women’s tournament game (around midday Eastern on the first Thursday/Friday of the tournament).

• Big platforms like ESPN, CBS, Yahoo: their rules say entries and changes must be completed before the first game’s tipoff; after that, all brackets lock.

So: check the rules of the specific site or pool you’re using, but as a safe rule, have your bracket done at least a couple of hours before the very first NCAA tournament game starts.