My personal rule is, If you must fly, then you must buy. This is the second question of this type we've had in the past couple months. Can't find the other thread at the moment, but my answer there was the same: Miles are great if you have a degree of flexibility. If you absolutely must travel on those dates and those specific flights (presumably you "need" to take these flights to mesh up with work or some other commitment) and a redemption ticket is not available now, you're better off buying a revenue ticket. If you can afford the currently available revenue fare but wouldn't be able to afford a higher fare later, you should probably pay now.