By about July of 2020 when Sia hits the 270,000 block height, there will be about 44.55 billion (((300,000+30,000)/2)x270,000=44.55 billion) Siacoins available in the market. From there, there will be about 1.57 billion (30,000x144x365=1.5678 billion) Siacoins created from the mining every year, forever.