A block confirmation is each new block added to the blockchain after the block that contains a specific transaction. The more confirmations a transaction has, the harder it becomes to reverse, making confirmations the primary measure of transaction finality in proof-of-work networks.
How It Works
When a transaction is first included in a mined block, it has one confirmation. When the next block is mined on top of that block, the transaction has two confirmations, and so on. Each new block effectively buries the transaction deeper into the chain’s history.
To reverse a confirmed transaction, an attacker would need to re-mine every block from the target block forward — a task that requires overwhelming the network’s total hashrate. With each additional confirmation, the computational cost of a reversal grows exponentially.
Confirmation Thresholds
Different platforms and use cases require different confirmation counts:
| Network | Typical Threshold | Approximate Time |
|---|---|---|
| Bitcoin | 6 confirmations | ~60 minutes |
| Ethereum | 12–32 confirmations | ~3–6 minutes |
| Litecoin | 12 confirmations | ~30 minutes |
| Exchange deposits | Varies by asset and exchange | Minutes to hours |
Six confirmations became the Bitcoin standard because the probability of a successful chain reorganization at that depth is vanishingly small — roughly 0.00002% even against an attacker with 30% of the network hashrate.
Confirmations vs. Finality
On proof-of-stake chains like post-Merge Ethereum, finality works differently. Rather than probabilistic security from stacked blocks, validators explicitly attest to blocks, and after two epochs (~12.8 minutes), transactions reach economic finality — they cannot be reversed without slashing at least one-third of all staked ETH.
History
- 2008 — Satoshi Nakamoto’s whitepaper introduces the concept of probabilistic finality through chained blocks.
- 2010 — Early Bitcoin exchanges begin requiring 6 confirmations for deposits, establishing the industry standard.
- 2022 — Ethereum’s Merge shifts finality from confirmation-based to attestation-based under proof-of-stake.
Common Misconceptions
“One confirmation means my transaction is completely safe.”
A single confirmation provides some security, but for high-value transactions, one block can still be reversed by a miner with significant hashrate. The six-confirmation standard exists precisely because one is not enough for meaningful protection against double-spend attacks.
Social Media Sentiment
Confirmation times are a frequent point of friction for users transferring funds between exchanges. During periods of high network congestion, slow confirmations generate complaints about gas fees and wait times. The topic resurfaces every time a 51% attack occurs on smaller chains.
Last updated: 2026-04
Related Terms
Sources
- Bitcoin Whitepaper — Section 11 — original analysis of confirmation probability.
- Investopedia — Confirmation — general overview of block confirmations.
- Ethereum.org — Finality — explains attestation-based finality vs. confirmations.
- Karol Trzeszczkowski — Confirmation Risk Calculator — mathematical model of attack success probability.