Confirmation

While a transaction is waiting in the mempoolGlossaryMempoolThe buffer in which a node collects valid but still unconfirmed transactions until a miner includes them in a block. There is no central mempool – every node keeps its own.On the learning path: Stage 5 · Step 4 – First withdrawal →In the glossary →×, it has 0 confirmations. Once it is in a block, it has its first; each further block adds one. Since a block is created every ten minutes on average, the number grows at roughly that pace.

Why more confirmations are safer

To reverse a confirmed payment, an attacker would have to recalculate its block and all the blocks after it – faster than the rest of the network. With 10% of the computing power, their chance of success after five blocks is below 0.1%, according to the whitepaper.^[1]

How many are enough?

That’s up to the recipient:^[2]

• 0 confirmations: not final. The transaction can still be replaced, for example via replace-by-feeGlossaryReplace-by-fee (RBF)A method of replacing a still-unconfirmed transaction with a new version that pays a higher fee. This lets you speed up a stuck payment, as long as it isn’t in a block yet.On the learning path: Stage 5 · Step 4 – First withdrawal →In the glossary →×. Never rely on it with strangers.
• 1 confirmation: the payment is in the blockchain, and the risk of a double spend drops sharply.
• 6 confirmations (about an hour): the common guideline for large amounts. The Bitcoin Developer Guide itself calls the number ‘somewhat arbitrary’.
• Exchanges and apps only credit deposits after a number of confirmations they set themselves. If a deposit takes a while, that’s often why.

Your first withdrawal to your own wallet shows how to check the status of a payment.