What Is a Bitcoin Confirmation?

When you send Bitcoin, your transaction is broadcast to the network and enters the mempool—a waiting area for unconfirmed transactions. Miners select transactions from the mempool, validate them, and include them in a new block. When your transaction is included in a block, it receives its first confirmation.

The blockchain is a sequence of blocks, each building on the previous one. Every new block added after the one containing your transaction adds another confirmation. After six blocks have been added on top of your transaction's block, it has six confirmations.

The Bitcoin white paper and community convention recommend six confirmations for high-value transactions. The reasoning is mathematical: to reverse a transaction with six confirmations, an attacker would need to rewrite six blocks—a task requiring more computing power than the rest of the network combined, executed faster than the honest network can produce new blocks.

For smaller transactions, fewer confirmations may be acceptable:

• 1 confirmation: Sufficient for small, everyday transactions
• 3 confirmations: Common for medium-value transactions
• 6 confirmations: Standard for large transactions and exchange deposits

Each confirmation exponentially increases the security of your transaction. After one confirmation, an attacker would need to mine a competing block faster than the honest network—a 51% attack. After six confirmations, the computing power required makes this practically impossible.

This is why exchanges often require three to six confirmations before crediting a deposit. It ensures the transaction is deeply embedded in the blockchain and cannot be reversed through a chain reorganization.

How long does one Bitcoin confirmation take?

On average, about 10 minutes. The Bitcoin network targets a 10-minute block interval, but this is an average—some blocks arrive faster, some slower. Your transaction must be included in a block to receive its first confirmation.

How many confirmations does an exchange require?

Most exchanges require three to six confirmations before crediting a Bitcoin deposit. This typically means waiting 30-60 minutes after sending. The exact number depends on the exchange's security policies.

Can a confirmed transaction be reversed?

Practically, no. After one confirmation, reversing a transaction requires a 51% attack. After six confirmations, the computing power required makes reversal effectively impossible. This is why six confirmations are considered the standard for final settlement.

What does 'unconfirmed' mean?

An unconfirmed transaction has been broadcast to the network but has not yet been included in a block. It is sitting in the mempool waiting for a miner to process it. Unconfirmed transactions can be replaced or may not confirm if the fee is too low.

Do I need to wait for confirmations to receive Bitcoin?

You can see the incoming transaction immediately in your wallet, but it will be marked as unconfirmed until a miner includes it in a block. For small amounts, you may treat one confirmation as sufficient. For larger amounts, wait for six confirmations before considering the transaction final.