With the new board structure I'm not sure where this question should go, since it's not related to a particular airline, but is related to frequent flier accounts..

I'm thinking about redeeming an award to London (Heathrow, probably) from the US. I understand if I redeem an award I'd have to pay the taxes. Approximately how much would that me? Does it vary depending on if I book a coach, biz or first ticket?

Thanks for any feedback.