Bitcoin is deflationary, meaning that mined coins are finite. Once miners unearth 21 million coins, that will be the total number of Bitcoins that will ever exist. But due to lost and forgotten wallets, active Bitcoins will be far lower than that. Total number of bitcoin users the 30th March 2015, Bitcoin reached the total circulation amount of 14 million coins.
There is now two thirds of the total amount of Bitcoins mined that there ever will be in existence. From this we may predict that there will be a rising price in bitcoin due to scarcity, over the long term, as the bounty for miners will be halved to 12. 5 BTC per block next year. 14 million bitcoins have been mined so far. This represents two thirds of the 21 million bitcoin limit. This second number is most likely to consist of lost coins. Bitcoins can be lost due to irrecoverable passwords, forgotten wallets from when Bitcoin was worth little, from hardware failure or because of the death of the bitcoin owner.
It’s extremely improbable and effectively impossible to recover lost coins. An interesting fact is that the person or group who created Bitcoin, Satoshi Nakamoto, has over one million coins that were mined during the early stages of the renowned crypto-currency. These bitcoins have remained unspent and moved, whether or not this was intentional or not, the motivation remains unknown. This pile of bitcoins accounts for one third of all inactive coins in existence.
Not a single satoshi has been moved or spent. Is there some cunning plan for these coins in the future? We will never know, but can assume after years and years of inactivity they are lost. This can be done by setting up a wallet with no known private key. The wallet can still be seen online, complete with every transaction, but the funds will likely never be retrieved. An example of a wallet like this that was created for no logical reason at all is Bitcoin Eater.