When to test

Kay

So I have a couple apps to monitor as and when I should expect my period. I haven’t been on any bc since April this year as I had the coil removed due to excruciating pains. We’re not actively ttc but none of the apps are syncing. Each says AF is due different days. We may of had a slip up this month but I have no idea when to test as I can’t even figure out when I’ll be late? Any ideas? My average cycle is 31 days and 5 days for AF.