Bitcoin and a few other early cryptocurrencies are unique in the fact that many people mining them and involved in the system early on thought they would never take off and didn’t bother to keep the wallets or the keys. Before silk road or mainstream exchanges like Mt. Gox, there wasn’t even really a price point or price discovery on a mass scale so to many they weren’t worth anything. There are handfuls of cases of people who mined or were given hundreds or thousands of coins and simply reformatted the hard drive the wallet was on, or threw out the wallet all together.
Other than the super early people, you had a long period of time where there were medium amounts of coins in the 1-10 bitcoin range that also suffered the same fate of being destroyed or just forgot about. I know personally that I lost about 2-3 bitcoin on a hard drive that I accidentally broke. There were also so many cases of people either sending to the wrong address or abandoning small amounts on addresses once they had made a transaction. So how many coins do we think are lost forever?
Satoshi’s coins are sort of up in the air, they haven’t been touched for close to 9 years at this point but they could still be accessible , we just don’t know. They would be about a million coins straight off the bat. From what we know, Satoshi only really ever spent about 50 btc and mostly just as a way to bring people in and show them the protocol. Even if we say Satoshi’s coins aren’t lost but simply just sitting on a hard drive somewhere, there are still a substantial amount unaccounted for.
If you simply google “lost bitcoins” you can see hundreds of stories of people losing coins that would be valued in the millions of dollars today. However because the bitcoin blockchain is available to see, we can see how many coins haven’t moved for x period of time. While there is no website that is openly putting block analysis stats for coins that haven’t moved for a period of time and are probably lost (that I know of), some people who work for analysis companies have said there is a good chance 10%-20% of all bitcoins are lost forever. This number I believe does count Satoshi’s coins, but even without, that number is substantial.
Im not a coder, but if I was I would love to see a website that looks at all the addresses and shows how many coins haven’t moved in x amount of years and put a likelihood of them being lost forever. Especially with the bitcoin cash fork, many addresses that did have access and simply just weren’t being touched, came forward to claim the new coins. This means that more than ever we are getting a clearer view of the amount that are lost. Bitcoin already has such a limited supply so the fact that many of them are lost and the fact that more are being lost every day through accidents, death, ect. means that they are getting rarer by the day.
Thanks to @Elyaque for the badges