Confirmation

How It Works

When you send a Bitcoin transaction, it first enters the mempool — a waiting area of unconfirmed transactions. Miners select transactions from the mempool (typically prioritizing higher fee rates) and include them in the next block they mine. Once your transaction is in a mined block, it has 1 confirmation. When the next block is mined on top of that block, your transaction has 2 confirmations, and so on. Each confirmation makes it exponentially harder to reverse the transaction.

The security of confirmations is rooted in proof-of-work. To reverse a transaction with 1 confirmation, an attacker would need to mine an alternative block with more proof-of-work than the honest chain. With 6 confirmations, the attacker would need to outpace the entire honest network for 6 consecutive blocks — an astronomically expensive endeavor even for nation-state actors against Bitcoin's current hash rate.

For practical use: zero confirmations should never be trusted for any amount. One confirmation is acceptable for small everyday transactions. Three confirmations provide very strong security for moderate amounts. Six confirmations have been the traditional standard for large transactions — this is what Satoshi originally recommended in the whitepaper. For exchange deposits and large settlements, most platforms require 3-6 confirmations.

Key Points

• Each confirmation is a new block mined on top of the block containing your transaction
• More confirmations make reversal exponentially more expensive for an attacker
• Zero confirmations should never be trusted — transactions can be replaced or dropped
• 1-3 confirmations sufficient for everyday amounts; 6 for large transactions
• Blocks are mined approximately every 10 minutes, so 6 confirmations take about 1 hour