New bitcoin follow a fixed issuance schedule
When a miner finds a valid block, the protocol allows new bitcoin to be created as the block subsidy. This is separate from the transaction fees the miner may also receive.
At the beginning of Bitcoin, the subsidy was 50 BTC per block. But the rules say that amount does not stay constant.
A halving happens every 210,000 blocks
After every 210,000 blocks, the block subsidy is cut in half. Because Bitcoin targets an average of roughly 10 minutes per block, a halving happens about every four years.
The sequence began at 50 BTC per block, then moved to 25, 12.5, 6.25, 3.125 BTC, and keeps shrinking.
That is where the limit comes from
Each subsidy level lasts for 210,000 blocks. So total issuance can be thought of as 210,000 × (50 + 25 + 12.5 + 6.25 + 3.125 + …).
That sequence gets smaller and smaller and converges on about 21 million BTC. The limit does not need a final switch that suddenly stops issuance — it follows from the issuance rule itself.
The 21 million are not created all at once
Supply increases gradually while the block subsidy continues. Each halving slows the creation of new bitcoin.
Halvings continue until the subsidy becomes zero at satoshi precision. That is expected to happen around the year 2140, not on one exact calendar date.
What happens after the final subsidy?
The end of new issuance does not mean mining or the Bitcoin network stops.
Miners can still be paid through transaction fees included in blocks. Exactly how that fee market will look so far into the future cannot be predicted with confidence today.
21 million does not mean 21 million available
The cap describes maximum issuance under Bitcoin’s rules. It does not mean every issued bitcoin will remain available to spend.
Some bitcoin may be permanently inaccessible because their keys were lost. They remain recorded on the network, but cannot be spent.
Frequently asked questions
Why was 21 million chosen?
For a beginner, the important point is that 21 million is the result of the issuance schedule: a 50 BTC starting subsidy, halvings every 210,000 blocks, and satoshi-level precision. Those rules produce the familiar cap.
Does the halving happen exactly every four years?
No. A halving is triggered every 210,000 blocks. About four years is an estimate based on Bitcoin targeting roughly 10 minutes per block.
Will there be exactly 21,000,000 BTC?
We usually say “21 million.” Technically, because the subsidy is expressed in whole satoshis and rounded down, total final issuance is slightly lower.
Can miners create more bitcoin by themselves?
Not under Bitcoin’s current rules. Nodes verify each block’s issuance and reject a block that creates more bitcoin than the rules allow.
What happens to miners when the subsidy reaches zero?
The protocol still allows transaction fees. Miners can be paid from those fees, while the shape of the fee market around 2140 cannot be predicted precisely today.