Why the price shown before a swap is different from the price you actually get

05 September 2026

The price you see before you confirm a swap is a snapshot from a moment in time, not a locked-in guarantee. The price you actually receive is the market price at the instant the swap executes, minus certain unavoidable costs.

Several things happen between the moment you see that price and the moment your trade settles. First, cryptocurrency prices move constantly. On volatile assets, the difference can be significant even within a few seconds. The quote displayed is based on the current order book or liquidity pool state when the page loaded. By the time your transaction is broadcast, validated, and executed on-chain, that state may have changed.

Second, the displayed price typically shows the raw exchange rate - what one unit of your source token is worth in the destination token. It does not include the spread. Every swap involves a spread: the difference between the highest price a buyer will pay and the lowest price a seller will accept. This is how market makers and liquidity providers earn. The spread is a cost of immediacy. You pay it to have your trade filled without waiting for a matching order.

Third, the quoted price often omits network fees. On Ethereum, for example, a swap triggers a smart contract interaction that costs gas. That gas fee goes to validators, not to the exchange. It is separate from the exchange's fee. The price you see usually shows the token exchange rate only. The actual amount you receive subtracts both the spread and the network fee from your output.

The exchange itself also charges a fee. That fee is often built into the quoted rate or added as a small percentage. Unidexai's fee structure is covered in the hub page "What a crypto swap actually costs" - that page explains how the exchange's cut works and how it compares to the spread and network costs.

Slippage is another factor. Slippage is the difference between the expected price of a trade and the price at which the trade actually executes. It happens when the trade size is large relative to the available liquidity. If you swap a large amount of a low-liquidity token, your own trade moves the price against you. The quoted price assumed a certain depth of liquidity; once your order starts filling, the price may shift. Most swap interfaces let you set a slippage tolerance. If the actual price moves beyond that tolerance, the transaction fails. That protects you but means the trade never happens.

Finally, the price shown is often a mid-market rate - the average of the best bid and ask. You never trade at the mid-market rate. You trade at the bid or ask, depending on which side you are on. The difference between the mid-market rate and the actual trade price is the effective spread.

In summary: the price before a swap is an estimate based on current market conditions, excluding spread, network fees, exchange fees, and slippage. The price you get is the real-time execution price minus all those costs. The gap can be small on liquid pairs with low volatility, or large on obscure tokens during rapid moves. To understand how all these costs stack up, read the hub page "What a crypto swap actually costs." It breaks down where every fraction of your swapped amount goes.

Back to crypto payments