One-sentence answer
The subsidy roughly halves every 210,000 blocks. Adding that declining series makes total issuance approach 21 million BTC.AT A GLANCE · EXPAND A STEP
01Initially 50 BTC per block
Validation rules limit the subsidy; miners cannot choose it freely.
02Halve every 210,000 blocks
50, 25, 12.5… the subsidy shrinks.
03Round in satoshis
Integer rounding eventually brings the subsidy to zero, just below 21 million BTC in total.
This diagram explains relationships, not the complete protocol implementation.
New issuance comes from the block subsidy
A valid 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.
calculate the maximum subsidy allowed at the current height and reject a that creates too much.
Halvings create a declining series
The original subsidy was 50 BTC per 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 time. The rule actually uses 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.
Try it: how the subsidy halves
50.00000000 BTC / block
Only the subsidy rule: halve every 210,000 blocks and round down in satoshis. Excludes fees; this is not a returns calculator. The subsidy reaches zero at halving 33.
CHECK YOUR UNDERSTANDING
Can a miner freely double the block subsidy?
A correct answer saves local progress. No account needed.View my learning pathThree 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.