# Bitcoin reorganizations: when a confirmed transaction changes branch 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. Evidence: [Bitcoin Developer Guide: Block Chain](https://developer.bitcoin.org/devguide/block_chain.html); [Bitcoin: A Peer-to-Peer Electronic Cash System](https://bitcoin.org/bitcoin.pdf) Canonical: https://degreesofsatoshi.com/encyclopedia/bitcoin-block-reorganizations/ Published: 2026-10-02 Substantively modified: 2026-10-02 Independently verified by an automated reviewer: 2026-10-02T18:15:23.891Z Data current through: 2026-10-02 AI-assisted research and drafting with a separate automated source-verification pass; no external expert or named human review is implied. ## Key facts - **Selection:** The relevant measure is accumulated proof of work, not simply a count of blocks. ([Bitcoin Developer Guide: Block Chain](https://developer.bitcoin.org/devguide/block_chain.html)) - **Depth:** Confirmations describe a transaction’s position in the chain currently accepted by the observer. ([Bitcoin Developer Guide: Block Chain](https://developer.bitcoin.org/devguide/block_chain.html)) - **Conflict:** A transaction from a displaced block is not guaranteed to confirm again. ([Bitcoin Developer Guide: Block Chain](https://developer.bitcoin.org/devguide/block_chain.html); [Bitcoin Developer Guide: Transactions](https://developer.bitcoin.org/devguide/transactions.html)) ## 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. Evidence: [Bitcoin Developer Guide: Block Chain](https://developer.bitcoin.org/devguide/block_chain.html) ## 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. Evidence: [Bitcoin Developer Guide: Transactions](https://developer.bitcoin.org/devguide/transactions.html); [Bitcoin Developer Guide: Block Chain](https://developer.bitcoin.org/devguide/block_chain.html) ## 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. Evidence: [Bitcoin: A Peer-to-Peer Electronic Cash System](https://bitcoin.org/bitcoin.pdf) ## Questions ### 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. Evidence: [Bitcoin Developer Guide: Block Chain](https://developer.bitcoin.org/devguide/block_chain.html); [Bitcoin Developer Guide: Transactions](https://developer.bitcoin.org/devguide/transactions.html) ## Claims and scope ### bitcoin-block-reorganizations-quick-answer 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: {"collection":"bitcoin","dataAsOf":"2026-10-02","blockHeight":null} ### bitcoin-block-reorganizations-fact-selection Selection: The relevant measure is accumulated proof of work, not simply a count of blocks. Scope: {"collection":"bitcoin","dataAsOf":"2026-10-02","blockHeight":null} ### bitcoin-block-reorganizations-fact-depth Depth: Confirmations describe a transaction’s position in the chain currently accepted by the observer. Scope: {"collection":"bitcoin","dataAsOf":"2026-10-02","blockHeight":null} ### bitcoin-block-reorganizations-fact-conflict Conflict: A transaction from a displaced block is not guaranteed to confirm again. Scope: {"collection":"bitcoin","dataAsOf":"2026-10-02","blockHeight":null} ## Sources - [Bitcoin Developer Guide: Block Chain](https://developer.bitcoin.org/devguide/block_chain.html) — Bitcoin developer documentation contributors. Block headers, transaction Merkle trees and competing valid branches. Locator: Proof Of Work; Block Height And Forking; Transaction Data. Retrieved: 2026-10-02T17:03:41.181Z. - [Bitcoin: A Peer-to-Peer Electronic Cash System](https://bitcoin.org/bitcoin.pdf) — Satoshi Nakamoto. Most-work chain selection, Merkle inclusion, SPV limits and transaction change. Locator: Sections 4–5 and 7–11. Retrieved: 2026-10-02T17:03:41.335Z. - [Bitcoin Developer Guide: Transactions](https://developer.bitcoin.org/devguide/transactions.html) — Bitcoin developer documentation contributors. UTXO inputs, transaction outputs, change and the difference paid as a fee. Locator: P2PKH Script Validation; Transaction Fees And Change. Retrieved: 2026-10-02T17:03:41.190Z. ## Revision history - 2026-10-02: Initial Bitcoin encyclopedia entry at this permanent URL. - 2026-10-02: Added reusable claims, explicit source locators, and matching Markdown and JSON. This publishing change does not itself establish factual verification. ## Cite this entry Degrees 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/