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The four costs inside one bridge transaction

A bridge transfer has a source gas fee, a destination gas fee, a protocol fee and often a liquidity spread. Four costs, usually quoted as one.

By FBT Swap · 5 October 2026

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        Source gas
        Fixed per transfer, paid in the source chain native coin
      
        Destination gas
        Usually bundled into the quote by the bridge
      
        Protocol fee
        A percentage with a minimum — the minimum hurts small transfers

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What you should know

Bridging looks like a transfer and is priced like a trade. The single number a bridge shows you is an aggregate, and knowing its parts is how you tell a reasonable quote from a bad one.

It also explains why bridging a small amount is often worse value than bridging a large one — some of the costs are fixed.

Gas on both sides

You pay gas on the source chain to lock, burn or deposit. Something then has to execute on the destination chain to mint or release, and that costs gas too. Most bridges pay the destination gas for you and bill it inside the quote.

These two are fixed per transfer, so they dominate small amounts and become negligible on large ones.

The protocol fee

The bridge charges for the service, typically as a percentage with a minimum. The minimum is what makes very small transfers uneconomic, and it is often the part that is easiest to miss in a quote shown as a single output figure.

Comparing bridges means comparing the final amount received, not the advertised percentage.

Liquidity spread on fast routes

A fast bridge does not wait for finality. It pays you immediately from a pool on the destination chain and settles later. That liquidity has a cost, and it appears as a spread between what you send and what arrives.

The spread widens when the route is imbalanced — if everyone is moving in one direction, the pool on the receiving side is depleted and the price of immediacy rises.

Deciding whether to bridge at all

Sometimes the cheaper path is not to bridge: swap into a stablecoin, move it via a route you already use, or simply trade on the chain where your funds already are. The point of a multi-chain interface is that the second option is usually available.

And bridging carries risk that a swap does not — bridge contracts have been among the largest single points of loss in crypto. The guide on bridge risk covers that in detail.

At a glance

Source gas

Fixed per transfer, paid in the source chain native coin

Destination gas

Usually bundled into the quote by the bridge

Protocol fee

A percentage with a minimum — the minimum hurts small transfers

Liquidity spread

The price of immediacy on fast routes; widens when imbalanced

FAQ

Frequently asked questions

Clear answers before you decide.

Why did I receive less than the amount I sent?

Because the quote nets out destination gas, the protocol fee and any liquidity spread. Compare bridges on the amount received, not on the headline percentage.

Is a slower bridge cheaper?

Often, yes. Canonical routes that wait for finality avoid paying for someone else's liquidity, so they cost less and take longer. Optimistic rollup withdrawals are the extreme case — cheapest and measured in days.

Can a bridge transfer fail halfway?

The usual failure is a delay rather than a loss, with funds recoverable once the route clears. Genuine loss has happened through bridge contract exploits, which is a different and much more serious risk class.

Risk notice

Crypto assets are volatile and on-chain transactions cannot be reversed. You can lose money, including all of it. Nothing here is financial advice.