I have been looking to get tickets to go to Mumbai from DC in Feb 2007. I have looked to depart on either the 4th, 5th or 6th and return 8 or 9 days after.

At one point I found a fare which was $775 with taxes from DC - London (Virgin) and then London to Mumbai (bmi). I should have grabbed at it then but obviously did not.

Right now I can find the same fare for about $900 while Delta is at about 1200. I just want to know how often these prices change and is there a way to predict these changes?