What day to start cyclical progesterone? 30-31 day cycle.

I have a 30-31 day cycle. ( almost all of the time-There can also be fluctuation in that) I know about when I ovulate (like a 4 day window) but I don’t know for sure what day it is. I am to start progesterone for 14 days a month. My provider kept saying to start on day 12, but I kept telling her it’s very unlikely I ovulate on day 12 and for me it is most likely more like day 16. If I start on day 12 I would be done on day 26.

When do you all start yours? The day after you ovulate? I’m thinking I’ll need to get those strips to make sure I hit the right day. Thank you!!!