The exact number of lost bitcoins is unknown, as there is no way to distinguish between lost coins and those that have been intentionally saved and not moved for a long time. However, it is estimated that around 4 million bitcoins are lost or inaccessible due to various reasons, such as lost private keys, forgotten passwords, or the death of the owner without passing on the access to the coins. This represents approximately 19% of the total bitcoin supply, which is currently capped at 21 million coins.