What is confirmation?

A record that a transaction has been included in a block, with each additional block on top counting as another confirmation.

Inclusion in a block is one confirmation. Every block built on top adds one more, and the count is a measure of how expensive it would be to reverse the transaction through a chain reorganization. That is why exchanges wait for a number rather than for a duration.

The number required varies by asset and by exchange, and it is set by the exchange's own risk policy rather than by any protocol rule. This is the single most common reason a deposit takes far longer than a block time suggests.

How it works

A transaction sits in the mempool until a miner or validator includes it in a block. At that moment it has one confirmation. It is included, not settled.

Each subsequent block makes reversal harder. On a proof-of-work chain an attacker rewriting history must redo the work of every block since, so the cost grows with each confirmation and the required number scales inversely with the chain's hash rate. This is why exchanges demand a handful of confirmations for Bitcoin and dozens or hundreds for smaller proof-of-work chains.

On chains with explicit finality the logic changes. Ethereum's checkpoint finality means a transaction becomes irreversible once finalized, so a venue can credit on finality rather than on a block count. See finality.

Fee level decides how long you wait for the first confirmation, not how many you need. An underpaid transaction can sit unconfirmed for hours during congestion, which is a different problem with a different fix.

Example

Illustrative. An exchange requires 3 confirmations for Bitcoin and 64 for a smaller chain. Your Bitcoin deposit confirms in the next block, roughly ten minutes, and credits about thirty minutes after that when the third block arrives. On the smaller chain with two-minute blocks, 64 confirmations is over two hours despite the faster blocks. The faster chain takes longer to credit, because the exchange is pricing the cost of reorganizing each chain rather than the clock.

Why it matters when you buy

If you are moving funds between venues to buy something, the confirmation requirement is the real transfer time and it is rarely displayed until after you send. Requirements vary between exchanges for the same asset, and stablecoin transfers on a fast chain are usually the quickest route. The exchange pages note deposit handling, and how to use a block explorer shows how to track confirmations yourself.

Related terms

chain reorganization — what confirmations protect against; finality — the stronger guarantee on some chains; mempool — where a transaction waits for the first one; block — what each confirmation is; double spend — the attack the count prevents.

Questions

How many confirmations are enough?

That is the exchange's judgment, not a protocol constant, and it reflects how expensive reorganizing that particular chain would be. Larger amounts and smaller chains attract higher requirements.

Why is my deposit still pending after it confirmed?

Because the exchange requires more than one confirmation, and possibly because it batches credits or reviews larger deposits manually. The block explorer shows the chain's view, not the exchange's queue.

Can I speed up confirmations?

You can speed up the first one by paying a higher fee, or by using replace-by-fee or child pays for parent if the transaction is already stuck. You cannot speed up the ones after it, since those arrive at the chain's own block rate.