What bitcoin’s rules promise, and what they don’t
Bitcoin is a set of rules that thousands of computers enforce at once. Here is what those rules actually guarantee, in plain terms, and where the guarantees stop.
Most arguments about bitcoin are really arguments about its rules: who wrote them, who can change them and what they guarantee. You can check most of the answers yourself, because the rules are public. Here is what they say.
A fixed supply, released on a schedule
There will never be more than 21 million bitcoin. New coins enter only one way: as a reward to whoever adds the next block of transactions to the ledger. That reward started at 50 bitcoin per block in 2009 and is cut in half every 210,000 blocks, roughly every four years. Since the April 2024 halving it has been 3.125 bitcoin. More than 20 million have now been issued, and the last fraction of a coin is expected around the year 2140.
Compare the dollar. The Federal Reserve and the banking system can expand the money supply when policy calls for it. The broad measure of U.S. money, M2, grew about 40% between early 2020 and its 2022 peak. Whether that was the right call is a policy debate. The point is that it was a decision someone could make. In bitcoin, no one can make it.
| Period | Reward per block | Coins issued in period |
|---|---|---|
| 2009 to 2012 | 50 | 10.5M |
| 2012 to 2016 | 25 | 5.25M |
| 2016 to 2020 | 12.5 | 2.625M |
| 2020 to 2024 | 6.25 | 1.3125M |
| 2024 to ~2028 | 3.125 | 656,250 |
| Every period after | Half the last | Half the last |
Each period is 210,000 blocks. Half of all bitcoin was issued in the first four years; each period after adds half as much as the one before, so the total approaches 21 million without reaching it.
Proof of work: why the ledger is hard to fake
To add a block, a miner has to find a number that, combined with the block’s contents, produces a result below a target. There is no shortcut: the only way to find it is to guess, trillions of times a second, and every guess costs electricity. Anyone can check a winning answer instantly.
That cost is the security. To rewrite past transactions, an attacker would have to redo the work for those blocks and outpace everyone else still mining, which today would mean controlling more computing power than the rest of the network combined. Every 2,016 blocks, about two weeks, the network adjusts the target so blocks keep arriving about every ten minutes no matter how much computing power joins or leaves. I explain the business side of that race in Bitcoin mining in plain English.
No one in charge, so changes are slow
Thousands of independent computers, called nodes, each keep a full copy of the ledger and check every block against the rules. A block that breaks a rule, say by paying a miner too much, is rejected by every node that sees it, regardless of who mined it.
That is why the rules are hard to change. The software can be upgraded, but an upgrade only takes hold if the people running nodes choose to install it. It has happened: SegWit in 2017 and Taproot in 2021 both changed how transactions work. Proposals to raise the supply cap have never come close, because almost no one running a node would accept them.
What the rules don’t promise
- A stable price. The supply is fixed, so changes in demand show up entirely in the price. Bitcoin has fallen more than 70% from a peak several times.
- Privacy. Every transaction is public and permanent. Addresses aren’t names, but once an address is linked to you, through an exchange account for example, anyone can follow the money.
- Safety at a company that holds it for you. The rules protect coins on the ledger, not promises made by a business. Customers of Mt. Gox in 2014 and FTX in 2022 learned the difference. How to hold bitcoin yourself is the subject of Six ways to hold bitcoin.
- Forgiveness for mistakes. There is no reversal button. Send to the wrong address or lose your keys and the coins are gone.
The short version
Bitcoin’s rules guarantee a fixed supply on a known schedule, a ledger that is expensive to rewrite and a system no single party controls. They don’t guarantee what the coins will be worth, who can see your transactions, or that anyone will help you if something goes wrong. Both halves matter.
Adapted from essays I wrote for the Kingdom Bitcoin newsletter between November 2025 and January 2026, rewritten here as a plain explainer. Supply figures follow from the protocol’s published rules. M2 figures are from the Federal Reserve’s M2 series. Nothing here is investment advice.
Questions about any of this? Email me at jlraney99@gmail.com.