when miners mine a block of bitcoin, they receive a reward. this reward gets cut in half every 210,000 blocks, which occurs roughly once every 4 years. during bitcoin's inception, the block reward was 50 btc. it was halved to 25 btc on november 28th, 2012, and to 12.5 btc on july 9th, 2016. as of may 11th, 2020, the block reward has been 6.25 btc.