A cross-chain swap costs four things: a transaction on the source network, a route or swap charge, price impact, and delivery on the destination network. Add them together to estimate what will arrive. The quoted exchange rate alone can hide costs paid on either chain.
1. Count the source transaction and any approval
The source transaction is the first cost: it pays the network to process your deposit or swap request. On Ethereum, this payment is called gas. It depends on how much work the transaction needs and how busy the network is.
Some tokens need a separate approval transaction before a service can use them. That means two source-network payments instead of one. On Arbitrum, a transaction can also include a charge for data posted to Ethereum, so a low layer 2 fee estimate may not tell the whole story.
Check which coin pays the source fee and whether your wallet already has enough. If you plan to send $500 worth of a token but have no ETH for an Ethereum transaction, the token balance alone cannot cover the fee.
2. Separate route charges from the exchange rate
A cross-chain route may involve a charge for moving funds, swapping them, or both. A swap can also include a pool fee: a charge paid when assets are exchanged through a liquidity pool, which holds tokens for traders. These costs may be taken from the input or the amount you receive.
Look for the estimated amount delivered, then compare it with the input after accounting for network costs. For a live comparison, you would use biswap.uk to check how much arrives after the route moves and exchanges the asset.
If you are weighing a route that moves and swaps assets in one flow, Biswap is a practical case to price from the amount delivered, rather than from the exchange rate alone. That keeps the route charge and any swap costs in the same comparison.
3. Estimate price impact on your trade size
Price impact is the way your own trade changes the exchange rate as it passes through a pool. A larger trade against a smaller pool usually has more impact. Slippage is the difference between the expected and final rate; it can grow if prices move before the swap completes.
For example, say a $500 trade has 0.4% price impact. That is about $2 less value before separate charges. A route showing a better rate for a tiny trade may give less for $500 if its available pool is shallow.
Biswap should be compared on the same input amount and destination asset as any other route. A quote for $50 cannot show how a $500 trade will affect the rate.
4. Include destination delivery in the total
The destination network may charge for the final transaction that delivers your asset. The route can subtract this cost from the output, so the receiving wallet may get less than the swap estimate. The destination fee can also change with network demand.
Say a route starts with $500, charges $1.20 on the source, $1.50 in route and pool charges, has 0.4% price impact, and costs $0.35 to deliver. The rough result is $494.95 before market movement: $500 minus $1.20, $1.50, $2, and $0.35.
Compare that estimated final value across routes. A route with cheaper source gas can still deliver less if its price impact or destination charge is higher.
Questions to check before you send
Why is the final amount lower than the quote?
The displayed amount may be an estimate before the destination transaction finishes. Network demand, a changing exchange rate, pool fees, and price impact can all affect the delivered amount. Check whether the quote includes both network fees and whether it shows an expected amount or a minimum amount you will receive.
Should I split a large swap into smaller trades?
Splitting can reduce price impact when a single trade is large compared with the pool. But every extra transaction may add network fees, and the rate can change between trades. Compare the estimated final amount for the full trade with the total expected output and fees for smaller trades.
Which balance should I keep for network fees?
Keep the native coin used for fees on the source network, and check whether the destination network needs a separate balance for later transactions. For example, ETH pays fees on Ethereum, while a token sent there does not automatically cover those fees. The fee coin depends on the network and the transaction.
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