Why does a swap quote change between the preview screen and the confirmation screen

05 September 2026

The quote changes because the market moved, or because the quote itself was never a binding price. In most cases, it is a little of both. The preview screen shows an estimate, not a promise.

Here is what happens between the two screens. When you first ask for a quote, the exchanger looks at the current order book and calculates an approximate rate. That rate includes its spread, plus a guess at the network fee. The number you see is a snapshot. It is valid for a moment, sometimes for a few seconds, rarely for a minute. The underlying market does not stop moving just because you are reading. Every new trade, every large order, every sudden spike in network congestion changes the real cost of executing your swap. By the time you click confirm, the snapshot is stale.

The confirmation screen, by contrast, shows the price the exchanger is actually willing to honour at that instant. It is a firm quote, but it is still a quote. It can change again if you hesitate. The exchanger locks the rate only for a very short window, often measured in seconds. If you take longer, the quote expires, and you get a fresh one. That is not a trick. It is how any market maker avoids taking a loss on a price that no longer exists.

Another reason is the network fee. The preview screen often shows a fee estimate based on average conditions. Between the preview and the confirmation, the mempool can fill up. Miners raise their minimum thresholds. The exchanger must pay more to get your transaction included in a reasonable time. That extra cost gets passed to you. The quoted amount you receive drops accordingly. Conversely, if the network clears, the fee estimate may fall, and you receive slightly more than the preview suggested. Neither direction is a guarantee.

There is also a technical layer. The preview screen may display a mid-market rate, or a rate from a cached feed, while the confirmation screen uses a live feed from the liquidity provider. The two can differ by a few basis points even when nothing dramatic happens. The difference is usually small, but it is real. The confirmation screen is the one that matters, because that is the number the exchanger will actually execute against.

Some exchanges include a slippage tolerance in the preview. They show you the worst-case amount, not the expected amount. Others do the opposite. They show an ideal rate and then apply slippage only at the final step. The result is the same: the two numbers rarely match exactly. The preview is a guide. The confirmation is a contract.

One more factor deserves mention. The quote you see on the preview screen often excludes the spread. The spread is the difference between the buy and sell price of the asset pair. It is how the exchanger earns its cut. The confirmation screen adds that spread into the final rate. So even if the market does not move at all, the confirmation amount will be slightly less than the preview amount. That is not a bug. It is the cost of doing business.

What can you do about it? Accept that the confirmation quote is the real one. If the difference is larger than a fraction of a percent, the market is moving quickly, or the network is congested. That is not a reason to panic, but it is a reason to act fast or to wait. The longer you sit between the two screens, the more likely the quote will shift. The best practice is to read the confirmation carefully, compare it to the preview, and decide if the change is acceptable. If it is not, cancel and try again.

For a fuller picture of where that difference goes, read the hub page, "What a crypto swap actually costs". It lays out the components - spread, network fees, and the gap between quoted and received - in one place. The short version is already visible here: the quote changes because the price is alive, the fee is an estimate, and the spread is always added at the end. None of that is hidden. It is just fast.

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