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What is a confirmation?
A confirmation is a count of how many blocks have been added since a transaction was included in the blockchain. One confirmation means it is in a block; each new block on top adds one more. On Bitcoin a new block arrives about every 10 minutes on average, with no guaranteed delay.
What it means for you
A transaction is not irreversible the moment it appears; each confirmation makes it harder to reverse. Bitcoin.org describes six confirmations as a minimum for high-value transfers, so a payment with zero or one confirmation is still provisional.
A common mistake: “If my wallet shows the incoming payment, it has arrived.”
In fact: A wallet can show a payment at zero confirmations. Bitcoin.org notes unconfirmed transactions are not secure; until a block includes it, the payment can still fail to arrive.
How it works
A transaction gains its first confirmation when a block includes it; every later block built on top adds one. Reversing it would mean redoing the proof-of-work for that block and every block after it, then overtaking the honest chain. The Bitcoin whitepaper calculates that the chance of a slower attacker catching up falls exponentially with each block: an attacker with 10% of the hash power has under a 0.1% chance once a payment is 5 blocks deep. Bitcoin.org rates one confirmation somewhat reliable, three mostly reliable, and six the minimum for high-value transfers.
An example
Say you sell something for bitcoin and the payment shows 0 confirmations: it is still pending. After the next block it has 1. At about 10 minutes per block on average, it would typically reach 6 in about an hour, though blocks can come faster or slower, and a low fee can delay the first one.
Sources: bitcoin.org: Some things you need to know, Bitcoin: A Peer-to-Peer Electronic Cash System (Nakamoto) · checked 4 October 2026
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Educational content, not financial advice. Written by hand and checked against the source named above. Something wrong? Tell us and we reply within two business days.