To fully mine the very last whole bitcoin it will take approximately the same time of mining the first 20,943,044 bitcoins (i.e. about 34 years)
According to estimates, bitcoin will reach its final coin figure sometime in 2140.
At the time of writing, more than 3 out of every 4 bitcoins that will ever exist have already been mined. Current block height is 517369
The total number of bitcoins, as mentioned earlier, has an asymptote at 21 million, due to a side-effect of the data structure of the blockchain - specifically the integer storage type of the transaction output, this exact value would have been 20,999,999.9769 bitcoin.
The first 50 BTC, included in the genesis block, cannot be spent as its transaction is not in the global database.
The Bitcoin block mining reward halves every 210,000 blocks, the coin reward will decrease from current 12.5 to 6.25 coins.
Next Reward-Drop ETA date: 30 May 2020 13:33:40 (in 782 days)