Reading on-chain
When is a crypto payment truly final?
In banking, final is a legal agreement. On a blockchain it is a probability that strengthens with every block — except on networks with explicit finality.
Probabilistic finality on bitcoin
Bitcoin has no official point of irreversibility; reversal simply becomes exponentially more expensive with depth.
Exchanges therefore set thresholds as a risk choice, not a technical rule.
Explicit finality under proof-of-stake
Ethereum finalises after roughly two epochs, about thirteen minutes, after which reversal would require destroying an enormous amount of staked ether.
Other networks finalise in seconds, usually with different decentralisation assumptions.
- Bitcoin: deeper blocks are safer
- Ethereum: finality after about two epochs
- Exchange thresholds are policy, not physics
Reorgs and why they are rare
A reorganisation happens when two valid blocks appear at once; transactions in the losing block return to the mempool.
One-block reorgs happen; deeper ones are rare and expensive.
Practical rules
Set waiting time by amount and context, and communicate it before the trade.
Frequently asked questions
How many confirmations are safe?
One for small bitcoin amounts, three to six for large ones; on Ethereum, finality after about thirteen minutes.
Can a confirmed transaction disappear?
Only in a reorg, and practically never once several blocks sit on top.
Why does my exchange wait so long?
It carries the reversal risk and therefore picks a conservative threshold.
Read next
Reading a transaction in the block explorer
Hash, confirmations, gas, status and addresses: what every field means and how to judge a stuck transaction.
The mempool: the network's waiting room
How the queue of unconfirmed transactions works, how to pick the right fee and what to do when stuck.
On-chain data: what actually means something?
Which on-chain numbers say something about real usage and which are mostly noise, with the pitfalls per metric.