Keep enough of each network’s fee coin to send the swap and use what arrives. A cross-chain swap moves value from one blockchain to another, sometimes changing the asset along the way. The fee for using a network is called gas, and each network may require a different coin to pay it.
Which balance pays each fee?
Your wallet needs the source network’s fee coin to start the move. Knowing which network sends the funds and which receives them helps you follow how to swap across chains with super bridge, because the two sides can have different fee rules.
- Check the network holding your starting asset. Leave its fee coin in your wallet for the first transaction; sending a token usually costs gas in the network’s own coin. On Ethereum, for example, fees are paid in Ether (ETH), even when you send a different token.
- Check the destination network and the asset you expect to receive. A received token may not be the coin that pays for another transaction there. If you plan to trade or send it again, you may need some of that network’s fee coin too.
How much gas should you leave?
Use the fee estimate for the action you plan to take, then leave a small cushion for a changing fee. A flat amount cannot fit every swap: the fee depends on the network, the work the transaction does, and how busy the network is.
- Before approving, read the wallet’s fee estimate and confirm the sending wallet still has enough fee coin after the swap amount is set aside. Ethereum.org explains that gas measures computing work, while the fee also depends on the current price of that work. Its guide gives around 65,000 gas units for a typical token transfer; a swap or bridge action can use more, so that figure is not a fee quote.
- Decide whether you need to act on the destination right away. If the route handles the destination step for you, you may not need destination gas just to receive the asset. If you want to trade or send it onward, keep enough fee coin there for that separate transaction. Check what the route’s estimate includes.
What should you check before signing?
Compare the amount you will spend with the amount you can use after arrival. The quoted receive amount may be a token that cannot pay gas, and network fees can change while you prepare the transaction.
- Leave the source fee coin untouched until the transaction is confirmed. If the wallet warns that the balance is too low, reduce the swap amount or add fee coin before signing; otherwise, the transaction may fail before it starts.
- For example, if a route sends about $500 worth of a token to another network, do not assume that token covers a later transfer. A cross-chain bridge and swap service such as super bridge moves and swaps assets across networks in one flow; check whether you also need the destination network’s fee coin for what you want to do next.