How much will be ETH inflation once it moves to PoS?

Let's assume ETH is a PoS coin now and all holders are staking and get 4% APY. If I hold $1000 in ETH at the end of the year i will have $1040 worth ETH. My question is – where did the $40 ETH that I earned by staking come from? Did they print/create new ETH? If yes, does anyone know how much will be the ETH inflation in such sceanrios?