You may get various responses telling you X or Y weeks/months ahead of time is the best but the reality is that there is no way for anyone to determine what the 'best' time will be. Do a Google search for 'dynamic airline pricing' and you will see that prices nowadays change in real time, just like the price of gasoline. They go up and down based on various factors and airlines today use complicated algorithms to determine the price someone will be willing to pay at any given point in time. By, in real time, I mean they can even change from one hour to another. So chasing the 'best' time to buy is like trying to predict the best time to buy on the stock market.

I tend to take a different approach to it. I get a rough idea of the price RANGE that a flight tends to fall within and I then decide on how much I am willing to pay based on that range. Let's say I see prices to X varying by month between $500 and $1500. I might decide I am willing to pay as much as $1000 IF I can find a flight that suits me, for the date I want to fly on. I go looking for that price and if I find it, I book it. So in other words, I determine what it is worth to ME to take that flight. Funnily enough, that is exactly what 'dynamic pricing' attempts to do, predict what price a person will be willing to pay at any given point in time.

I also take into account a few other factors that matter to me besides price. I will pay more for a non-stop flight than one with one or more layovers. I will pay a bit more for some extra legroom. There are certain airlines I will not fly with regardless of their price. Regarding when I book, I do so only after I am quite positive nothing is likely to interfere with my going. So for example, I would never book 6 months or more ahead of time. That's just too far in advance for me to feel sure nothing will interfere with me going. I tend to book around 4-8 weeks ahead of time. The timing of the booking dependent on my being ready to book, not on when someone guesses the airline will post their lowest price.