The first transaction in every block, created by the miner, pays out the new-coin subsidy plus all fees. Learn its special rules and famous messages.
The first transaction in every block
Every block begins with one special transaction: the coinbase. (It has nothing to do with the company of the same name.) It is how new bitcoin enters circulation.
What makes it special
- It has exactly one input, which doesn't spend any previous output. Instead the input contains arbitrary data, the "coinbase field".
- Its outputs may pay up to the subsidy + all fees in the block. Paying more makes the block invalid.
- Its outputs can't be spent until 100 more blocks are mined ("coinbase maturity").
- Since 2012 (BIP 34) the coinbase field must start with the block height.
Messages in the coinbase
Miners often write text into the coinbase field, such as their pool's name. The genesis block famously contains a newspaper headline. See The genesis block.
See one now
Open the latest block on MyBitcoinExplorer and click its first transaction. You'll see:
- No real input: just the coinbase field with the block height and often a pool name.
- One or more outputs paying the miner or pool.
- An OP_RETURN output holding the SegWit witness commitment.
Messages written by miners
Pools often write their name in the coinbase field. MyBitcoinExplorer shows such text only as untrusted content: anyone can write anything there.
Key takeaways
- The coinbase is the first transaction in a block and creates new bitcoin.
- It can pay at most the subsidy plus the block's fees.
- Its outputs are spendable only after 100 more blocks.
Common questions
Why can't coinbase outputs be spent right away?
If the block were replaced in a reorg, those coins would disappear. Waiting 100 blocks makes that practically impossible.
Do miners always claim the full reward?
Almost always. A few blocks have claimed slightly less by mistake, and those sats are lost forever.
Is the coinbase transaction related to the company Coinbase?
No. The company took its name from this transaction type.
Why does the coinbase have an OP_RETURN output?
Since SegWit it carries the witness commitment, the hash committing to all witness data in the block.