The short answer
A Bitcoin confirmation means a valid transaction is inside a block that a node accepts as part of Bitcoin's active proof-of-work chain. The block containing it gives the first confirmation. Each block built after that adds one more.
That count is evidence that changing the transaction's history would require replacing the work behind its block and the blocks after it. It is not a promise that reversal has become impossible. The Bitcoin white paper explains that later blocks reinforce an earlier timestamp and that the probability of a competing chain catching up falls as blocks are added.
How confirmations are counted
Bitcoin Core 31.1 is the latest non-prerelease release checked on 26 October 2026. Its
getrawtransaction implementation
counts confirmations as one plus the active chain tip height minus the transaction's block
height. If a transaction is in block 999,998 while the tip is 1,000,000, it has three
confirmations: its own block plus the next two.
A transaction in a node's mempool has zero confirmations. It has been seen and may be valid under that node's policy, but no accepted block contains it yet. Seeing the same transaction in several wallets or block explorers does not turn it into a confirmation.
How to check the status
- Copy the transaction ID from the sending or receiving wallet.
- Confirm the wallet is synced and set to the intended network.
- Open the transaction details and look for a block height or block hash.
- Read the confirmation count. Zero means unconfirmed; one means included in the latest accepted block; a rising count means later blocks are extending that chain.
The expected result is agreement between the count and the displayed block information. If the count does not rise, first check whether the wallet is still syncing. If the transaction disappears or is marked conflicted, inspect whether another transaction spent the same inputs.
What confirmations do not guarantee
Before confirmation, a transaction can be replaced under node policy or removed from a mempool. BIP 125 documents one replacement policy and warns recipients about relying on replaceable unconfirmed payments.
After confirmation, a chain reorganization can move the transaction out of the active chain. More confirmations make that outcome progressively harder, not logically impossible. There is no universal safe number for every payment. The amount, what is being delivered and the recipient's risk tolerance determine how much evidence is enough.