One-sentence answer
The block subsidy roughly halves every 210,000 blocks. Adding that declining series makes total issuance approach 21 million BTC.New issuance comes from the block subsidy
A valid block can include a special coinbase transaction assigning the allowed subsidy and transaction fees to the miner. New BTC comes from the subsidy; fees transfer existing BTC.
Nodes calculate the maximum subsidy allowed at the current height and reject a block that creates too much.
Halvings create a declining series
The original subsidy was 50 BTC per block and it halves about every 210,000 blocks: 50, 25, 12.5, 6.25, and so on. Adding all eras produces a limit approaching 21 million.
“Every four years” is a convenient estimate based on average block time. The rule actually uses block height.
Can the rule change?
Developers can propose code, but they cannot remotely upgrade every node. A node that has not adopted a higher-supply rule will reject blocks that exceed its local limit.
This is not a claim that software rules are physically immutable. It means one organization cannot unilaterally command all participants to accept a change.
Three things to remember
- ✓New issuance is the subsidy; transaction fees are not new supply.
- ✓The limit follows from a geometric halving schedule.
- ✓Nodes reject blocks that create more than their local rules allow.
A common follow-up
Will exactly 21 million BTC exist?
No. Issuance continues, and details such as integer rounding mean the final spendable total will be slightly below exactly 21 million.
Primary sources
Primary sources
These links lead to protocol material, developer documentation, or open-source code—not trading services.