This is a great question and one that many people wonder about. You will often see it written as bitcoin, while other times you will see it written as Bitcoin. Which one is correct? Well, both of these spellings are correct. You can generally call it either Bitcoin or bitcoin and no one will mind. But there is a general method which differentiates the two spellings. While it is not common yet, it may soon be the norm to spell it differently based on what you are referring to.
When people talk about Bitcoin, they aren’t just talking about the currency. Often they are talking about the whole payment system or the network. In general practice, if you are writing about the currency you can just write bitcoins. You can say that this house is worth a thousand bitcoins and that will be perfectly fine. On the other hand, if you were to write about the Bitcoin payment network, or about how Bitcoin’s infrastructure needs to be updated, you should use the capital B.
Right now none of these are the correct or incorrect usage. Over time, we may decide which spelling we are more comfortable with. If this seems too arbitrary a way of determining spelling, that is because it is. Language doesn’t really play by any rules – it evolves according to how it is used. We are just talking about capitalization here, but often the whole meaning of the words changes because of how they are used.
Now, this question raises another question. Generally whenever we use a proper noun, we capitalize it. When we write ‘currency’, we just say currency, but when it is a name of a currency, we typically capitalize it. Why then do we insist on writing ‘bitcoin’ the way we do? A good answer to that is right in the bitcoin logo.
As you can see, the logo most commonly associated with bitcoin spells it without capitalizing the b. Combine this with the fact that the tech industry loves using small letters (remember when AT&T became at&t for no reason?) and you end up with most people spelling it as ‘bitcoin’. It is just more convenient to write it without having to capitalize the first letter.
Then there is the fact that you will see it written in both ways, and you will see different people using it in different ways. We aren’t talking about just your average internet commentators; you will see this disparity even in professional writers. Basically, there is no rule set for bitcoin yet. You can write Bitcoin or bitcoin and no one is going to call you out on it. The best practice however would be to only use Bitcoin when you talk about the system or about the network. If you are talking about the currency or if you are denoting how many units of the currency something costs, you should just use bitcoin.