Community post

Sometimes our bodies decide to switch things up. It could be possible that you ovulated that day.

Sounds like you ovulated early. I did with my last cycle, like 5 days early and got pregnant.

If u normally O on cd17 of a 31 day cycle, then if u were to O on cd13, which is 4 days earlier than ur norm, u would expect af that many days earlier. So a cd17 O gives u a 14 day luteal phase, so O'ing on cd13 with a 14 day lp would make ur new cycle length 27 days (+/- 1-2 days becuz ur lp can vary a bit from cycle to cycle). In short, yes u can O cd13, but ur cycle will no longer be 31 days.
Good luck! =))

My fertility book says for a 31 day cycle start testing on cycle day 14, so I think it is possible you O'ed on cycle day 13. Not out of the realms of impossible