Stage One: Days Shown On Screen
The first stage is to work out how many separate days are shown on screen during the movie. So here's a good old-fashioned list of them:
Day 1: Groundhog Day Day 2: The first repetition Day 3: The fixed pencil Day 4: Punching Ned Day 5: Deceiving Nancy Day 6: Robbing the bank Day 7: Seeing Heidi 2 with a French Maid Days 8-12: Engineering the near-perfect date Day 13: The bad perfect date Days 14-21: One for every slap Day 22: "Phil you look terrible!" Day 23: Jeopardy Day 24: "This is pitiful!" Days 25-27: Breaking the alarm clock Day 28: Kidnapping Punxsutawney Phil Day 29-31: Phil's suicides Day 32: I'm a God! Days 33- 35: First piano lessons Day 36: Sexually harassing Ned Day 37: Looking after the homeless man Day 38: The final Groundhog Day
So, by my reckoning that's 38 separate days shown in the movie. This is of course assuming that every separate thing listed above happens on separate days, which I think isn't too much of a dangerous assumption, given that Phil is something of a quitter (case in point: multiple attempts at suicide).
Second, and far more difficult stage is to take things Phil says as indicators for other days we do not see. Jump over to page two to find out how we work that out...