A cross-chain swap quote estimates how much you will receive after your crypto moves between blockchains. The final amount can change before the trade completes because prices, available liquidity, and network costs can shift.
Why can the amount change after I get a quote?
A quote is based on conditions at one moment; it is not a guaranteed exchange rate. On a centralised exchange, a limit order can wait for a chosen price. A wallet-based swap usually submits a trade against available liquidity, meaning crypto set aside for trades.
The trade itself can move the pool price. This effect is called price impact: swapping a large amount against a small pool usually gives a worse rate than swapping a small amount against a deep pool. For example, a $200 trade may barely affect a pool, while a $20,000 trade through the same pool may shift its price noticeably.
There can also be movement while the trade is underway. A cross-chain route may need a transaction on the source chain to confirm before the destination asset is sent. If the market or available pool balances change during that wait, the eventual output can differ from the estimate. A BTC-to-ETH route such as thor swap is a practical example: you send BTC and receive ETH, but the quoted amount reflects conditions when the route is priced.
What does slippage tolerance protect?
Slippage tolerance is the maximum price movement you agree to accept before the swap should stop. The swap sets a minimum output, meaning the least amount of the destination asset you will accept. If execution would fall below that floor, the trade may fail or the input may be returned, depending on the route.
For example, if a quote says you should receive 1 ETH, a 1% tolerance sets a floor near 0.99 ETH. A wider tolerance may let the trade complete after a larger price move, but it also allows you to receive less. A tighter tolerance protects your price more, yet a fast-moving market can make the trade fail.
Price impact and slippage tolerance are related, but they are not the same. Price impact comes from your trade size against available liquidity; tolerance is the limit you set for extra movement after the quote. A large trade can have high price impact even when the market is still.
What should I check before sending?
Compare the expected output with the minimum output, and check whether the estimate includes network costs. You may pay a fee on the source chain to send the asset and another on the destination chain to deliver it. These costs vary with network demand, so the amount left in your wallet can differ from the swap output.
I would compare the minimum output for the full amount, not just the headline rate. If a large trade has a poor floor, try a smaller amount or wait for deeper liquidity; splitting it can add extra network costs, so compare the total before choosing.