Typically taxes like this are levied on the amount above the threshold. So someone making $250,000 / year will have to pay $0 in additional taxes. This is just like the federal income tax, where if you go into the next bracket you don't suddenly have to pay more on everything up to that bracket. It is only the additional income that is taxed at the higher rate. It's amazing how many intelligent conservatives don't understand this basic aspect of taxes in the US. If you make more you always keep more in the US.