Reserve Gas Before a Cross-Chain Swap

A cross-chain swap needs gas on the source chain when you submit it, and may need a separate fee or gas allowance on the destination chain when it completes. Keep the source chain’s native token in your wallet, even if you are swapping the rest of your balance into another asset.

Ethereum.org explains that Ethereum transaction fees are paid in ETH, and the fee applies even if a transaction fails. A route may bundle several steps, such as token approval and the swap, so read its quote and wallet prompts before signing; the guide to choosing a ParaSwap bridge or cross-chain swap covers how routes differ.

How much gas should you reserve on the source chain?

Reserve enough native token for every transaction the route asks you to send. The exact amount depends on the chain, current network fees, and the route’s steps, so use the wallet’s estimate and leave a margin instead of relying on a fixed amount from an old quote.

Check whether the wallet asks for a token approval before the swap. If approval is a separate transaction, it costs gas separately; an existing approval may avoid that step, depending on the token and route. Do not assume the swap amount shown is also the amount available for fees.

Does the destination chain need gas too?

It depends on how the route handles delivery. Some routes may deliver the destination token and leave you to pay for later transactions in that chain’s native token; others may offer a way to cover or arrange destination gas as part of the service.

Before confirming, check the quote for the destination asset, estimated delivery, fees, and any stated gas support. If gas is not covered, reserve the destination chain’s native token separately before you need to move or swap the delivered asset.

What should you check before signing?

Review each wallet prompt against the route’s stated steps. A practical check is:

• Keep native gas on the source chain for approval and submission.
• Confirm the network and destination address shown in the quote.
• Check whether destination gas is included, sponsored, or left to you.
• Leave a balance for fees rather than swapping every available token.

Ethereum.org says unused gas is returned, while fees for gas already used are still paid; a failed transaction can therefore consume some of your reserve. A route’s estimate can change with network conditions, so refresh it before signing and compare the final wallet prompt with the quote.

Once the source transaction is submitted, the route’s status page or wallet should show whether delivery is pending or complete. The destination gas arrangement can vary by route, so confirm it in the current quote before sending; the actual delivery time may remain unconfirmed until the transfer finishes.