So I was sitting here reading an article about securing your wallet, and I just started to wonder how many times someone has screwed up and lost their wallet.dat either by mal-intent or self-stupidity.
There can only be 21 million, but how many have already been lost forever? Isn't it possible that someone had 100 BTC in 2010 and then said "meh, this thing sucks" and just deleted the files from their computer? After all, it wasn't worth much back then so why try to sell a meager 100 BTC at that time?
Is there a way to determine how many lost Bitcoins there are?
/end random thoughts
there is this search box at the top of the page, use it to find "known lost bitcoins" to get an idea of how many bitcoins are lost for sure, you can guestimate as well as anybody else how many more are unknown lost bitcoins. You could also do some reading on the "bitcoin days destroyed" metric which can help estimate how many old coins are moving, the moving of old coins is the only way to know for sure they have not been lost this whole time.