Hey friends advice needed!

Sophia
I'm 28, trying to conceive 1st baby, my period cycles have been so crazy so I don't know how to judge when I'm most fertile. Most recent cycle was 48 days, before that was 41 days, before that was 38 days, before that was 30 days. So I have no idea when is best to try to conceive! Which number do I go off when I put it into an aviation calculator? 
Any help / advice would be super appreciated!! ❤️