Bitcoin is a virtual currency designed for deflation, with total supply cap of 21 million.
When designing Bitcoin, Satoshi set each Bitcoin to be divisible to 0.00000001. The block reward was 50 Bitcoins, and such reward will be halved every 210,000 blocks. If a new block is generated every 10 minutes, it will take around four years to mine 210,000 blocks.
Since 2009, the block reward has been halved twice, the block reward is currently 12.5 Bitcoins. Around Year 2045, 99.95% of Bitcoins will be issued, and the last Bitcoin would be mined in the year 2140, reaching the total supply of 21 million. (Note: The actual figure is 20999999.97690000)
The fundamental soundness of Bitcoin’s deflationary nature has caused quite a debate among economists, but this mechanism has encouraged miners to start sooner than later, which provides processing power and security to the network.