Why Bridge Relayers Charge an Extra Execution Fee

A bridge relayer’s execution fee helps pay for the transaction that completes a transfer on the destination chain. The fee is separate from the gas you pay to start the transfer, because a relayer may submit a second transaction on your behalf. Knowing what that fee covers helps you compare the amount you send with the amount you’ll receive.

What does a bridge relayer do?

A relayer carries proof of a confirmed transfer to the destination chain and submits the transaction needed to finish it. Depending on the bridge, that may release or mint the bridged asset, or trigger another action. A relayer is a service or operator that submits this transaction; it does not make the two chains one network.

For a business, the steps can include moving funds between wallets or accounting for a transfer across chains. This guide to how Mantle Bridge moves business funds covers that process in more detail. The transfer itself may take time while the source transaction is confirmed and the destination step is prepared.

What does the execution fee pay for?

Usually, the fee covers some or all of the gas for the destination transaction, plus a payment to the relayer for providing the service. Gas is the network charge for processing a transaction. The relayer often pays that charge first, then recovers it from the fee attached to the bridge transfer.

The exact breakdown depends on the bridge. A quote may include an estimate of destination gas, a buffer for changes before execution, and the relayer’s service margin. If the destination transaction does more work—for example, it includes a swap or a contract call—it may need more gas than a simple token transfer. Those extra steps can also bring separate fees.

This is different from the gas you pay on the source chain to start the transfer. Check whether the bridge quote shows both charges, and look at the amount expected to arrive after fees.

Why does the fee change between transfers?

The destination chain’s gas price can rise or fall while a transfer is waiting to be completed. Relayers may also estimate costs differently, and some charge more for a service that handles extra steps. So the same transfer amount can come with a different execution fee at another time or through another route.

Before sending, check the quote for:

• The source-chain gas charged to start the transfer.
• The relayer or execution fee and which chain it covers.
• The estimated amount you’ll receive, including any swap or service charges.

Can a bridge transfer avoid the relayer fee?

Some bridge designs let users complete the destination step themselves, which can avoid paying a relayer’s service margin. But the user still needs to submit a transaction and pay destination-chain gas, and may need the destination chain’s native token to do it. A relayed route bundles that work into the transfer, which can be simpler when you want the funds delivered without managing a second transaction.

Compare the final amount received and the steps required, not just the fee label. An execution fee is not automatically an extra charge for the same transaction: in a relayed route, it helps pay for a separate transaction that completes the transfer.