Why a BTC-to-ETH swap can return less ETH

A BTC-to-ETH swap can return less ETH than its quote because fees, available liquidity and price changes affect the trade before it settles. The number shown at the start is usually an estimate, not a promise. For a fuller look at how one cross-chain route works, see thor swap. The key is to compare the estimate with the minimum amount you agree to receive.

Why does a swap quote change?

A quote changes when the market moves or the trade uses up available liquidity. Liquidity means the assets ready in a market or pool to complete swaps. A large trade can move the price more than a small one, especially when there are fewer assets available.

For example, a route may estimate that your BTC is worth a certain amount of ETH when you begin. If the BTC or ETH price shifts before the swap finishes, the final amount can differ. A busy network can add delay, giving prices more time to move.

Slippage is the difference between the expected price and the price a trade gets. Swap services often let you set a slippage limit or show a minimum received amount. If the trade cannot meet that minimum, it may fail instead of completing at a worse rate.

What fees reduce the ETH you receive?

A cross-chain swap can involve costs on more than one network. Bitcoin needs a network fee to send BTC, and Ethereum needs a fee to send ETH to your wallet. The route may also charge a service or liquidity fee. Some quotes include these costs in the estimated output; others show them separately.

• Network fees: Pay miners or validators to process transactions on each chain.
• Swap fees: Pay the service or liquidity providers that make the conversion possible.
• Price impact: The trade itself can shift the rate when available liquidity is limited.
• Wallet or route costs: Extra steps in a multi-network route may add fees or affect the estimate.

Check whether the displayed ETH amount is before or after fees. A quote with a better headline rate may leave you with less after costs than a slightly worse rate with fees already included.

How can you tell what amount is guaranteed?

Usually, the only firm limit is the minimum output shown when you approve the swap. The estimate can change, while the minimum states how much ETH you will accept for the trade to proceed. It is a floor for execution, not a promise that the swap will complete.

Before sending BTC, check the expected amount, the minimum received, the fees and the destination wallet address. Make sure the route supports the wallet and network you plan to use. If the minimum is too low for you, adjust the slippage setting or wait for a steadier quote.

The practical takeaway is simple: treat the quote as a snapshot, then judge the swap by its minimum output and total fees. That gives you a clearer sense of what you may receive and when it is better to let the trade fail.