Keep Gas on Both Chains Before Your First Cross-Chain Swap

Before a first cross-chain swap, keep the source chain’s gas token in your wallet and plan for possible fees on the destination chain. Gas is paid in a network’s native token, so holding the asset you want to swap may not cover the transaction.

The route determines which networks and steps are involved. A Biswap guide to choosing a cross-chain route covers that choice in more detail; the practical point here is to check the fees for each step before you send funds.

Which gas tokens should I keep?

Keep the native gas token for every network where your wallet must submit a transaction. Ethereum transactions use ETH, while other networks have their own fee tokens; Ethereum.org’s gas documentation explains that fees are paid in the network’s native currency.

A cross-chain route may require an approval and a swap or bridge transaction on the source network. It may also require a separate transaction after funds arrive, such as swapping the received asset or moving it again. Some routes handle destination steps through a relayer, so check the route’s fee breakdown rather than assuming every destination action needs your own gas.

• Check the source network and its required fee token.
• Check whether the route includes an approval transaction.
• Check if the destination action is handled for you or requires a wallet transaction.
• Leave a small reserve for a retry or later transaction; don’t spend the full balance on the swap.

How much gas should I leave?

Use the wallet’s current estimate for each transaction, then leave extra in the relevant gas token. There is no reliable fixed amount for every swap: fees vary with network conditions, and contract calls such as approvals and swaps use more gas than a simple transfer.

Review the fee estimate immediately before confirming. On Ethereum, the total fee depends on gas used and the fee per unit, which changes with network demand. A low-cost route can still be a poor fit if it leaves you without enough native tokens to complete the next step.

What should I check before sending?

Confirm the source and destination networks, the asset and amount, and which fees the route deducts from the transfer. Make sure the wallet shows enough gas on the source chain before signing; if a destination transaction is yours to submit, retain that chain’s gas token too.

For a first swap, choose a route whose steps and fees are clear, and keep a reserve on each network where you may need to act. Check the final wallet prompt and route status before starting another transaction.