What is finality?

The point at which a confirmed transaction can no longer be reversed by the network.

Proof-of-work chains approach it probabilistically, so deeper blocks are safer, while Ethereum finalizes checkpoints after two epochs, roughly thirteen minutes. Exchange deposit rules are set from this, which is why crediting times differ by asset.

The distinction that matters is between confirmed and final. A transaction in a block is confirmed. Whether it is final depends on what it would cost someone to remove that block, and on some networks the answer is still "not very much" several blocks later.

How it works

Two designs give two different guarantees.

On a proof of work chain, nothing is ever mathematically final. Each additional block makes reversal exponentially more expensive, because an attacker must redo that work and outpace the honest network. Security is therefore a probability that improves with depth, which is why the practical rule is a number of confirmations rather than a state.

On Ethereum's proof of stake design, finality is explicit. Validators vote on checkpoints at epoch boundaries, and a checkpoint becomes finalized once two consecutive epochs have justified it (source: the Ethereum consensus specifications). Since an epoch is 32 slots of 12 seconds, that is 12.8 minutes. Reverting a finalized checkpoint would require validators holding at least a third of the total stake to sign conflicting messages, and the protocol destroys their stake for doing so; see slashing.

Rollups add a third case. A transaction can be effectively settled on a layer 2 within seconds according to that network's sequencer, while final on the base chain only after the rollup's proof or challenge process completes. An optimistic rollup withdrawal delay of several days exists for exactly this reason; see fraud proof.

Exchanges translate all of this into a confirmation count per asset, which is why the same deposit size waits a different length of time on different networks.

Example

Illustrative comparison of how long the same deposit waits. A network producing a block every ten minutes and requiring 3 confirmations takes about 30 minutes. A network producing a block every 2 seconds and requiring 64 confirmations takes about 2 minutes. The second is faster in wall-clock time and the security behind each confirmation is not the same, which is precisely why the counts differ.

Why it matters when you buy

Withdrawal and deposit times you experience come straight from finality rules plus the venue's own policy, and no amount of paying extra shortens them. Check the network's characteristics at the chain pages and the venue's stated confirmation requirements at the exchange pages.

Related terms

confirmation — the count that approaches finality, chain reorganization — what finality prevents, epoch — the unit Ethereum finalizes in, slashing — the penalty securing it, double spend — the attack it defeats, fraud proof — why rollup withdrawals wait.

Questions

How many confirmations are enough?

That is set by whoever is accepting the transaction, and it varies by network and by amount. Exchanges publish their own requirement per asset, and it is the number that governs when your deposit credits.

Is Ethereum final faster than Bitcoin?

Ethereum gives an explicit finality guarantee after roughly thirteen minutes. Bitcoin never gives an explicit one, only a probability that becomes overwhelming with depth. They are different kinds of assurance rather than points on one scale.

Why does my layer-2 transaction settle instantly but withdraw slowly?

The rollup's sequencer accepts it immediately, while the base chain only treats it as final after the network's proof or challenge window completes. The withdrawal waits for the second event, not the first.