I hope you mean taxing additional income that much, otherwise earning 40k$ instead of 1$ less would make you pay 40k$(25%-20%)=2000$ more in taxes, which means people would have to start checking how much they´ve earned when closing to yearend, and sometimes working less (or asking for less pay) to not go to the next bracket. Why not just use a function? Like, tax rate=lesser of: 0.25earnings,40% or something like that. My personal favourite is basic income+flat tax rate though.