# Why there will only be 21 million bitcoin

New bitcoin is issued on a fixed schedule that halves every 210,000 blocks. See the maths behind the 21 million cap and who enforces it.

Canonical page: https://mybitcoinexplorer.com/learn/bitcoin-supply-21-million
Topic: Bitcoin basics
Published: 2026-10-29
Updated: 2026-10-30


## A fixed schedule
New bitcoin only enters circulation through the [The block reward](https://mybitcoinexplorer.com/learn/block-reward) paid to miners. That reward started at 50 BTC per block and **halves every 210,000 blocks**, roughly every four years. See [The Bitcoin halving](https://mybitcoinexplorer.com/learn/bitcoin-halving).

> Diagram: Total bitcoin in existence over time, approaching but never reaching 21 million — 

## The maths
Each four-year period adds half as much as the one before:

- 210,000 × 50 = 10,500,000 BTC
- 210,000 × 25 = 5,250,000 BTC
- 210,000 × 12.5 = 2,625,000 BTC
- …and so on.

10.5 + 5.25 + 2.625 + … gets closer and closer to 21 million. Because rewards are counted in whole [satoshis](https://mybitcoinexplorer.com/learn/satoshis-and-bitcoin-units) and rounded down, the real total ends just under it: about **20,999,999.98 BTC**. The last new satoshi is expected to be mined around the year 2140.

## Who enforces the cap?
Every [full node](https://mybitcoinexplorer.com/learn/what-is-a-bitcoin-node). If a miner tries to pay themselves more than the allowed reward, nodes reject the block, and the miner loses the reward entirely. The cap isn't a promise from a company; it's a rule every node checks.

> Some coins are permanently lost (forgotten keys, the unspendable [The genesis block](https://mybitcoinexplorer.com/learn/genesis-block) reward), so the amount actually usable will be lower than 21 million.


## How much exists today?
By late 2026, after four halvings, about 20.1 million bitcoin had been issued: over 95% of everything that will ever exist. The remaining coins will take more than a century to mine because each halving slows issuance.

## Can you check the supply yourself?
Yes. A full node can total every unspent output: Bitcoin Core's `gettxoutsetinfo` command reports the exact amount in existence, and it matches the schedule. No company report is needed, which is one reason people trust the cap. See [What is a Bitcoin node?](https://mybitcoinexplorer.com/learn/what-is-a-bitcoin-node).

## Lost coins
Coins locked to keys nobody has can never move again: forgotten passwords, destroyed hard drives, early experiments, and the genesis reward. Estimates of lost coins vary widely, but they mean the usable supply is smaller than the issued supply.


## Key takeaways

- The block reward halves every 210,000 blocks.
- Total supply approaches but never exceeds about 20,999,999.98 BTC.
- Nodes reject any block that pays too much, which enforces the cap.

## Common questions

### Can the 21 million limit be changed?

Only if nearly all users chose to run software with different rules. Nodes running today's software would reject such blocks, so in practice the cap is very hard to change.

### What happens when all bitcoin is mined?

Miners will be paid only by transaction fees.

### When will the last bitcoin be mined?

Around the year 2140, when the block subsidy reaches zero satoshis.

### What happens if bitcoin is lost?

It stays on the blockchain but can never be spent, which slightly reduces the usable supply.

## Related lessons

- [The Bitcoin halving](https://mybitcoinexplorer.com/learn/bitcoin-halving)
- [The block reward](https://mybitcoinexplorer.com/learn/block-reward)
- [Where does new bitcoin come from?](https://mybitcoinexplorer.com/learn/where-does-new-bitcoin-come-from)
- [Consensus rules](https://mybitcoinexplorer.com/learn/consensus-rules)