What Bitcoin is, and why 21 million matters

Bitcoin is money that no company, bank or government runs. It’s a shared record of who owns what, kept by thousands of computers around the world that all check each other’s work. This guide covers the basics you need before you think about wallets or storage.

A shared ledger nobody owns

Every bitcoin transaction ever made is written into one public record called the blockchain. A new page, called a block, is added about every ten minutes.

Anyone can run the software that keeps a copy of this record. Those computers are called nodes. Each node checks every new block against the rules on its own. If someone tries to spend coins they don’t have, or create coins out of thin air, the nodes reject it. No single node is in charge, which is why nobody can quietly change the rules or the history.

How new bitcoin is made

New bitcoin enters the system through mining. Miners use specialized computers to compete for the right to add the next block. The winner earns newly created bitcoin plus the fees from the transactions in that block.

The amount of new bitcoin per block is cut in half roughly every four years. This event is called the halving. The last one was in April 2024, which cut the reward to 3.125 bitcoin per block. The next is expected around April 2028, at block 1,050,000.

Why 21 million matters

Because the reward keeps halving, the total number of bitcoin can never pass 21 million. The last fraction of a coin is expected to be mined around the year 2140. The 20 millionth bitcoin was mined in March 2026. About 20.1 million exist as of November 2026.

That cap is written into the rules every node enforces. Changing it would require nearly everyone running the network to agree to dilute their own holdings, which is why most people treat it as permanent.

The supply is fixed, but each bitcoin splits into 100 million smaller units called sats (short for satoshis). You never need to buy a whole coin.

This is where the name of this site comes from. Compare that to government money, where the supply can grow whenever a central bank decides it should. You don’t have to agree with any particular view of economics to see why a fixed, predictable supply appeals to people.

What “owning bitcoin” means

This is the part most people get wrong.

Your bitcoin doesn’t sit in an app or on a device. It sits on the shared ledger, assigned to addresses. What you actually own is a private key: a secret number that proves you’re allowed to spend from those addresses.

• Whoever has the private key controls the bitcoin.
• If you lose the key and its backup, the bitcoin is gone. No help desk can recover it.
• If someone else gets the key, they can spend your bitcoin, and the transaction can’t be reversed.

When you buy bitcoin on an exchange and leave it there, the exchange holds the keys. You hold a promise from the exchange. That’s why the community saying is “not your keys, not your coins.” The next guide, Keys, seeds and self-custody, explains this in detail.

What Bitcoin isn’t

A few common misunderstandings:

• It isn’t anonymous. Every transaction is public. Addresses aren’t tied to names by default, but exchanges collect ID, and transactions can often be traced. Treat it as public, not private.
• It isn’t controlled by its creator. Bitcoin was released in 2009 by someone using the name Satoshi Nakamoto, who stopped posting in 2011. Nobody has authority over it now.
• It isn’t “crypto” in general. Thousands of other coins exist. Most have a company or foundation behind them and no fixed supply. This site focuses on Bitcoin only.

What to read next

1. Keys, seeds and self-custody: what you’re actually protecting.
2. Hot wallets vs cold storage: where keys can live, and the trade-offs.
3. Practice on signet: run the full wallet process with free test coins.

Nothing on this site is financial advice. We don’t predict prices. We explain how Bitcoin works and how to hold it safely if you choose to.