How many block confirmations each chain needs before a swap completes

05 September 2026

The number of block confirmations required varies by chain, typically ranging from 1 to 30 blocks. Bitcoin usually needs 3 confirmations; Ethereum and most EVM chains require 12; Solana often completes with 1 to 2.

These numbers are not arbitrary. They reflect a trade-off between speed and finality. A block confirmation is a new block built on top of the block containing your transaction. The more confirmations that accumulate, the harder it becomes for an attacker to reverse that transaction by reorganising the chain.

Bitcoin works on a proof-of-work model where blocks arrive roughly every 10 minutes. One confirmation alone can be reversed if a miner with enough hash power builds a competing chain. The common standard of 6 confirmations is considered very secure for high-value transfers. For cross-chain swaps, many exchanges and protocols accept 3 confirmations as a reasonable balance. That is about 30 minutes of waiting.

Ethereum blocks come every 12 to 15 seconds. Its proof-of-stake finality mechanism means that after 12 confirmations (roughly 2.5 minutes), the probability of a reorganisation drops to near zero. Most swap services treat 12 confirmations as sufficient. Some accept fewer for smaller amounts, but 12 is the default.

Solana is different. Its block time is roughly 400 milliseconds, and its history proof mechanism means that most transactions reach finality in under a second. A single confirmation is typically enough for swap completion. Some services wait for 2 confirmations as a safety margin, but the wait is still under one second.

Litecoin, Dogecoin, and other Bitcoin-like chains follow a similar logic but with different block times and security assumptions. Litecoin blocks arrive every 2.5 minutes. Most services accept 3 to 6 confirmations. Dogecoin, with its 1-minute block time, often uses 3 confirmations.

Binance Smart Chain (BSC) and other EVM-compatible chains operate like Ethereum. They use 12 to 15 confirmations as the standard, though some services lower the threshold to 6. BSC's faster block time of 3 seconds means 12 confirmations take only 36 seconds.

Polygon, Avalanche C-chain, and Fantom also follow the EVM pattern. Their block times vary from 1 to 2 seconds. The 12-confirmation rule still applies, but the actual wait is shorter. A 12-confirmation wait on Polygon might be 24 seconds.

You may notice that none of these numbers are absolute. Services set their own thresholds. Some use dynamic confirmations: fewer for small swaps, more for large ones. Others rely on probabilistic finality, meaning they release funds after a certain number of confirmations even though the chance of reversal is not zero.

The key point is that the swap cannot complete until both sides have enough confirmations. If you send Bitcoin to the exchanger, it waits for 3 Bitcoin confirmations. Only then does it send the equivalent amount on the destination chain. That second transaction then needs its own confirmations on that chain before it reaches your wallet.

This waiting period is inherent to the security model of each blockchain. You cannot speed it up without accepting more risk. Some services offer "instant" swaps by fronting the funds and taking the risk themselves, but that is a different product.

For the broader picture of how these confirmations fit into the flow of transferring value without a centralised account or a bridge, see the hub page "Swapping crypto across chains." It explains the overall mechanism that makes these confirmations necessary.

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