Methods an apparatus for performing sub-carrier adaptation in multi-carrier communication systems. In one embodiment, a method includes receiving, via a reverse communication channel, a first data unit via multiple subcarriers. The method further includes determining an estimate of a forward communication channel based on the received first data unit. The method further includes determining different bit rates for the multiple subcarriers based on the estimate of the forward channel. The method further includes transmitting a second data unit via the multiple subcarriers, where bits in the second data unit are allocated across the multiple subcarriers based on the determined bit rates for the multiple subcarriers.