When two miners find a block at once, nodes briefly disagree, then all switch to the longer chain. Learn how reorganizations work and what they mean for you.
Two blocks at once
Blocks take seconds to spread across the world. Occasionally two miners find a valid block at the same height before hearing about each other. For a moment, half the network sees block A and half sees block B.
How it resolves
Miners keep working on whichever block they saw first. When the next block is found on top of A, A's branch has more work, and every node switches to it. Block B becomes stale (often called an "orphan").
Switching from one branch to another is a reorganization ("reorg"). Nodes undo B's transactions, apply A's branch, and return B's transactions to the mempool if they're still valid.
What it means for you
- A transaction with 1 confirmation can occasionally drop back to 0 if its block goes stale. It usually confirms again in the next block.
- Reorgs deeper than one or two blocks are very rare.
- That's why newly mined coins must wait 100 blocks before being spent. See The coinbase transaction.
How often does it happen?
One-block reorgs happen occasionally, typically a few times a month or less, because fast block relay makes simultaneous blocks rare. Two-block reorgs are very rare, and deeper ones are not expected on Bitcoin under normal conditions.
What MyBitcoinExplorer does
A reorganization changes which blocks are on the active chain. A disconnected block may be marked orphaned. Its transactions can return to the mempool if they remain valid and are accepted; transactions conflicting with the new chain may not return.
Key takeaways
- Two blocks at the same height can briefly coexist.
- Nodes switch to the branch with the most work; the other block becomes stale.
- Reorgs are why confirmations are counted and why big payments wait for several.
Common questions
Is a stale block the same as an orphan block?
In everyday use, yes. Strictly, orphan used to mean a block whose parent is unknown.
Do miners of stale blocks get paid?
No. Their coinbase reward exists only on the abandoned branch.
Do I lose money in a reorg?
Normally no. Your transaction returns to the mempool and confirms in a following block, unless someone deliberately double-spent it.
What is an orphan block?
Commonly another name for a stale block: a valid block that ended up off the main chain.