How far out to book flights?

are flights at their cheapest 6 or 8 weeks prior to flight?
Right now im still 3 months out, but I found a flight for $380 which is cheaper than yesterday, but last Sept our flight was only $230 RT . I booked it last year early and when it dropped I changed the flight and received the credit...which I might do again, but would rather not if I don't need to. eventho I am going to PHX in March and could use the credits then.....

 

There is no mathematical formula to flights I'm afraid. It's based on how full the plane is and how far away the flight is and presumably a load of other variables

 

Might I suggest the following site. Enter your planned destination and it will email you the best fares.

http://www.airfarewatchdog.com/