Why cross-chain swaps wait for the slower chain

A cross-chain swap must clear two blockchains, and the slower required confirmation step sets the earliest point your trade can finish. The swap service also needs to process the trade and send the asset on the destination chain.

Why does a cross-chain swap wait for confirmations?

Each blockchain keeps its own record of transactions. A swap service generally waits until the incoming transfer is confirmed before it treats those funds as ready to trade. That helps protect against a transfer being reversed or replaced before it settles.

Confirmation rules differ by chain and may depend on the size of the transfer. A Bitcoin transfer, for example, has to be recorded in blocks; an Ethereum transfer follows Ethereum’s own block and finality process. The service must follow the relevant rules for each leg, so the chain that takes longer to reach the required state can hold up the whole swap.

For a native BTC-to-ETH route, the incoming Bitcoin must be observed and processed before the service can arrange the outgoing ETH. The thor swap guide walks through that route in more detail. It helps to think of the swap as linked steps across separate ledgers, rather than one transaction that happens everywhere at once.

What else can make the slower leg take longer?

Confirmation time is only part of the wait. Once the incoming transfer is accepted, the swap service has to process the trade, and the destination network must include the outgoing transfer.

• Network activity: Busy chains can take longer to include transactions, especially when users compete for limited block space.
• Confirmation policy: A service may require more confirmations to reduce the risk of a reversal, particularly for larger transfers.
• Destination congestion: The outgoing transfer can wait for space on the chain where you want to receive funds.
• Swap settings: Some services let you trade faster or split a larger swap into smaller steps over time. The slower, price-focused option may take longer by design.

These steps are sequential in many swap designs: the service cannot safely act on an incoming transfer until its rules are met, and the destination transfer comes after the trade is processed. That means a fast source chain does not guarantee a fast arrival if the other leg is still waiting.

How can you tell what is holding up your swap?

Check the swap’s status or transaction tracker and identify which leg is pending. If the incoming transfer is still confirming, the wait is on the source chain or the service’s confirmation rule. If the trade is processed but the outgoing transfer is pending, the destination chain or the service’s processing queue is the likely hold-up.

Before sending, check that the source and destination networks match the route you selected, and keep the transaction ID. Avoid sending a second payment just because the first one is taking time; check its status first, since a delayed transaction may still complete.

Watch the next status change: confirmation of the incoming transfer tells you the swap can move to processing, while an outgoing transaction ID shows that the destination leg has begun.