Bitcoin confirmations and chain reorganizations
Count confirmations correctly and understand why a payment becomes harder to replace as more blocks follow it.
The quick answer
The first confirmation is the block that includes your transaction. Each following block adds one. A chain reorganization can replace recent blocks and change that count.
Finality increases with depth
Bitcoin nodes follow the valid chain with the most accumulated proof of work. Short competing tips can occur. An unconfirmed payment can conflict with another spend, and even confirmations are not an absolute mathematical guarantee.
Step by step
- 1
Check inclusion first
A broadcast transaction has zero confirmations. Find its block height only after it is included in the currently accepted chain.
- 2
Apply the receiver's policy
Choose a confirmation requirement that matches value and risk. Exchanges and merchants can set different rules.
- 3
Recheck after a disruption
If status changes or a reorganization is reported, consult your wallet and current chain data before delivering goods or sending a replacement.
Worked example
A transaction in block 100 has three confirmations when the chain tip is block 102: 102 − 100 + 1.
Before you continue
A related question
Does an unconfirmed payment reserve my balance forever?
No fixed global timer governs mempools. A transaction may be removed, replaced or rebroadcast. Check its inputs and any confirmed conflict before spending again.
Try it with a tool
Sources & further reading
Source links checked on 15 Oct 2026. Examples explain the mechanics; provider fees and features can change.
- Bitcoin Developer Guide developer.bitcoin.org
- Bitcoin.org bitcoin.org
