What is finality?
- Author
- CRYPTO PORT Editorial
- Published
- Updated
- Reading time
- 5 min
In short
Finality is the point at which a transaction can be considered irreversible. Bitcoin offers probabilistic finality — the odds of reversal shrink as blocks stack up — while Ethereum marks blocks as finalised once explicit conditions are met. The distinction decides when you may trust a payment.
Key points
- The state in which a transaction can no longer be reversed
- Probabilistic finality strengthens as blocks accumulate
- Deterministic finality declares a block final once rules are met
- Exchange confirmation requirements follow from this
Definition
The guarantee that a settled transaction will not later be undone. It comes in two forms: probabilistic, which strengthens over time, and deterministic, which is declared once specific conditions hold.
On Bitcoin any block can in principle be reversed, but doing so means rebuilding from that block and overtaking the existing chain — steadily less feasible as blocks pile on top. The convention of six confirmations is a practical judgement about when that risk becomes negligible.
Proof-of-stake Ethereum instead marks blocks as finalised through validator votes, normally two epochs — about thirteen minutes — after the block. Reversing a finalised block would require an attack large enough to get a great deal of staked ETH destroyed.
The practical lesson is simple. Treat a one-confirmation Bitcoin deposit as final and a reorganisation can leave you having shipped goods for a payment that no longer exists. Exchanges set different confirmation counts per asset precisely because finality differs by chain.
Watch out for
- · A 'received' notice in an app is not finality — wait for the required confirmations
- · On probabilistic chains, every confirmation you skip raises your reversal risk
- · Chains with little hash power or stake are easier to reverse at the same confirmation count