How early do you purchase airline tickets?

So I'm chomping at the bit to make plans but at four months things have the potential to change so much.

How far ahead do YOU purchase your plane tickets?

I'm flying in August (for visit) and September (for the move).

 :)Holly

i usually booked a few months in advance, a bit cheaper that way

I usually buy a couple of months ahead- I bought a ticket for a September move in July, and I bought the ticket for my early February visit in late November or early December.

I'd be more concerned with getting the August trip booked, if I were you. It's school holiday time and fares are likely to be higher. That's my impression, anyway. 

I would book as soon as possible - tickets for flights to the UK in August have already gone up by several hundred dollars in the last few months! Plus, with fuel cost increases, the cost of flying has gone up in the last few weeks - I've been thinking of flying to Hawaii to visit one of my friends at the end of this month. In March, the tickets were $550, but I didn't book then as I wasn't sure of dates. Now the tickets are almost $900 and I can't really afford to go .

When my parents want to book flights to the US for July or August, they usually try to book as soon as the prices are released -  in September or October of the year before! The prices are usually much cheaper then (often the price of a ticket increases as the number of seats available decreases).

thanks to all!

Yes, ksand, I've noticed that myself.  I've been tracking the cost for the last month and watched it go from $780, to $950, to $830, to $1100.  I KNEW I should have jumped on that $830!!! but I was being "cautious" in case plans changed!

BA has a non-stop going for $1100ish - I just have this nagging feeling that the day after I  book, some other airline with have a sale.  Arg.

I still don't know what dates I want exactly for visiting home over the summer, so I might have to go for last minute fares.  All of the "student discounts" seem really crap and barely discounted.  A lot of the cheap fares seem to be with BA, Virgin and Air India.