Conception and due date confusion

[Leleophants]

Hi, I'm really confused about exact ovulation and due dates. One app says Im in fertile week now. Another says I've started fertile window but ideal date is next week. Wouldn't conception then versus conception a few days ago mean a completely different due date? Despite my period having started at the same time?

I guess my question is, how many days after period is the 'best' day as maybe I'm just lucky if sperm survives and should really do it again later?
I dont know when to test either.

Really new to the whole thing!

If you've only just started tracking your cycles the apps will probably be using cycle day 14 as a guide as that's when ovulation usually happens, but every woman is different, I usually ovulate on cd16 but sometimes as late as cd21. Sperm can live for up to 5 days and the egg for about 24 hours I think, so that's why your apps are giving you a fertile window and just differ slightly. When your period starts if you count back 14 days then that's probably when you ovulated and the apps will become better at predicting when you'll ovulate if your cycles are the same length each month. I use Flo and it seems to be pretty accurate. Your due date will be calculated from the first day of your period no matter when you ovulated, until you have a scan and they'll measure baby to predict a due date. If you have sex every other day you're more likely to catch the egg at ovulation rather than waiting for ovulation or when the app says you'll be fertile.