lookup works using a binary search so it splits the data in half, tests if the lookup value is greater than the last value in the first half - if so it throws away the first half and repeats the process with what's left (if not, it throws away the second half and repeats with the first half) this continues until it finds a match or runs out of data. normally for lookup (and vlookup or hlookup with fourth argument set to TRUE) to work as you want, you need to sort the data so that the splitting works, but here the formula is looking for a value greater than any value in the list so will always end up with the last value.