Encyclopedia How the network works · Entry 96
Bitcoin reorganizations: when a confirmed transaction changes branch
In this article
At a glance
Key facts
| Fact | Detail | Source |
|---|---|---|
| Selection | The relevant measure is accumulated proof of work, not simply a count of blocks. | [1] |
| Depth | Confirmations describe a transaction’s position in the chain currently accepted by the observer. | [1] |
| Conflict | A transaction from a displaced block is not guaranteed to confirm again. | [1][3] |
How two competing tips can arise
Two miners can find valid blocks extending the same parent before either block has reached everyone. Different nodes may temporarily see different tips. A later extension can make one branch the preferred chain.
This temporary competition is different from a deliberate change to consensus rules. Nodes still validate the candidate branch under the rules they enforce.
Re-read the actual payment after a reorganization
A payment previously shown in a block may also be included in the replacement branch, possibly at another height. If it is absent and its inputs are still available, it may be eligible for rebroadcast. If the new chain contains a conflicting spend, that original payment cannot also spend the same outputs.
A wallet should evaluate the transaction and its inputs rather than assume every displaced payment simply returns to the same pending queue.
Depth reduces ordinary reversal risk without an absolute promise
The white paper models how an attacker’s chance of catching up changes with depth under specified hash-power assumptions. That model is not a universal guarantee for every network condition.
A confirmation policy depends on value, threat assumptions and tolerance for delay. No fixed number transforms proof-of-work settlement into mathematical irreversibility.
Direct answers
Questions people ask
Can a confirmation count go down?
Yes. It can change when the observer’s accepted chain changes. Check the transaction’s actual block location and whether a conflicting spend exists.
Inspect the evidence
The answer and key facts have stable claim links. These records retain the scope and qualification when reused.
A Bitcoin block reorganization occurs when a node changes its active chain to a competing valid branch with more accumulated proof of work. Blocks from the former branch stop contributing confirmations. Their transactions may appear in the new branch, become pending again or conflict with transactions now confirmed.
Scope: Bitcoin · data through 2026-10-02. Verification: verified · 2026-10-02T18:15:23.891Z.
Link to this claimSelection: The relevant measure is accumulated proof of work, not simply a count of blocks.
Scope: Bitcoin · data through 2026-10-02. Verification: verified · 2026-10-02T18:15:23.891Z.
Link to this claimDepth: Confirmations describe a transaction’s position in the chain currently accepted by the observer.
Scope: Bitcoin · data through 2026-10-02. Verification: verified · 2026-10-02T18:15:23.891Z.
Link to this claimConflict: A transaction from a displaced block is not guaranteed to confirm again.
Scope: Bitcoin · data through 2026-10-02. Verification: verified · 2026-10-02T18:15:23.891Z.
Link to this claimRevision history
- — Initial Bitcoin encyclopedia entry at this permanent URL.
- — Added reusable claims, explicit source locators, and matching Markdown and JSON. This publishing change does not itself establish factual verification.
Source register
Sources and references
Retrieval dates and locators are recorded individually.- Bitcoin Developer Guide: Block ChainBitcoin developer documentation contributors
Block headers, transaction Merkle trees and competing valid branches.
Locator: Proof Of Work; Block Height And Forking; Transaction Data · Retrieved: 2026-10-02T17:03:41.181ZOpen source - Bitcoin: A Peer-to-Peer Electronic Cash SystemSatoshi Nakamoto
Most-work chain selection, Merkle inclusion, SPV limits and transaction change.
Locator: Sections 4–5 and 7–11 · Version / scope: 2008 paper · Retrieved: 2026-10-02T17:03:41.335ZOpen source - Bitcoin Developer Guide: TransactionsBitcoin developer documentation contributors
UTXO inputs, transaction outputs, change and the difference paid as a fee.
Locator: P2PKH Script Validation; Transaction Fees And Change · Retrieved: 2026-10-02T17:03:41.190ZOpen source
Research and drafting use AI assistance. A separate automated review checks claims against primary sources; no external expert or named human review is implied. Publication, substantive editing, source retrieval and verification are recorded separately. This version was independently checked by an automated reviewer on 2 October 2026.
Editorial method and correctionsDegrees of Satoshi editorial project. “Bitcoin reorganizations: when a confirmed transaction changes branch.” Published 2026-10-02; updated 2026-10-02. https://degreesofsatoshi.com/encyclopedia/bitcoin-block-reorganizations/