I was using my app (glow) for about 6 months, logging info and everything I got pregnant but lost the baby at 5 weeks in July, I used the app again and got pregnant with this baby on September 7th according to the app. I'm sure it wasn't spot on but it was accurate enough.
I didn't use opks (ovulation prediction kits) I am just going by the dates on my period tracking app. according to it I ovulated on September the 7th. just fyi