Which day do I mark as O day?

[ashleyg]

I'm on CD 17 and took an OPK today...it showed up slightly darker than the one I took yesterday. I'm using Ovia to track ovulation, so when would I mark that I actually ovulated? Today?

 

[JGraefe]

If it were me I would mark CD 17 as your surge but I'm not an expert!

 

[DobbyForever]

Definitely the darker one. You o 24-36 hours after your first positive but more like 8-10 after your darkest. I also used that brand for almost two years, and I always had my o as the second day of positives/darkest positive confirmed by bbt. Fxed!