Happy Death Day: How Many Times Does Tree Die?

Stage One: Tree's Realisation

The film has a surprisingly lengthy opening sequence, which concludes with Tree being killed for the first time, as she's stabbed through the head in a tunnel while on her way to a party.

Tree then wakes up and repeats the same day, but in her haze of hungover confusion, isn't yet aware that she's trapped in a time loop. After repeating most aspects of her day, Tree decides to avoid the tunnel this time on her way to the party, but still ends up dead when the killer arrives at the party, kills her hookup Nick, and then stabs her with a broken bong.

This is where Tree begins to realise something's fishy, as she enters her third time living out the same day, and decides to stay home from the party entirely. However, the killer has stowed away in her bathroom and manages to stab her regardless. This is clearly the default death if Tree opts to do nothing with her day and just bum around watching Netflix in bed, for instance.

At this point in the movie, Tree has died 3 times, and there's no ambiguity regarding any additional deaths that could've sneaked in-between. This is about setting up the movie's gimmick and Tree figuring out what's going on, so there's no possibility of extra kills here.

But now, here's where things get a little more complicated...