Why do two people swapping the same pair at the same time get different amounts

05 September 2026

They get different amounts because the swap is priced against the actual liquidity available at that exact moment, and that liquidity can be different for each person. The two people are not really swapping the same pair at the same time - they are swapping fractions of a second apart, against a market that moved between their clicks.

The most important reason is that every swap consumes liquidity from the order book or the liquidity pool it uses. When the first person's swap goes through, it removes the best-priced tokens from the available supply. The second person then faces a slightly worse price because the cheapest orders are gone. On a quiet day, the difference might be small. On a busy day, one large swap can shift the rate by several percent, and the next person gets noticeably less.

A second reason is that the two people may not be swapping the same direction relative to the pool. One might be buying token A with token B, while the other is buying token B with token A. Even if they sent the same amount, the buy and sell sides of a liquidity pool are not symmetric. The pool's pricing curve is designed so that buying one token pushes its price up, and selling it pushes its price down. Two trades in opposite directions at the same time could actually produce very different results.

Third, the swap platform itself may route the two trades through different paths. Most swapping sites use an aggregator that checks multiple liquidity sources - decentralized exchanges, order books, private market makers - and picks the best combination for each specific swap. The first swap might be sent to a pool that has deep liquidity in the pair, while the second swap, milliseconds later, finds that pool depleted and gets routed through a less favorable source. The aggregator does not guarantee the same route for two orders, even if the user sees the same preview rate.

The quoted rate you see before confirming is not a guarantee. It is an estimate based on the state of the market when the preview loaded. By the time you confirm, that state has changed. The sibling page How do swapping sites decide the rate they show you explains exactly how that estimate is calculated and why it can differ from the executed rate.

Network fees can also cause a tiny difference. The first person might have paid a higher network fee to get their transaction mined quickly, which affects the net amount they receive after costs are deducted. The second person, using a lower fee, might get their transaction through later, at a different market price.

Finally, the amounts being swapped matter. A person swapping a small amount will typically get a rate very close to the mid-market price, because the trade does not move the market. A person swapping a large amount will push through multiple price levels, receiving a worse average rate. Two people sending different sizes at the same moment will get different amounts even if all other conditions are identical.

So the short answer is: they are not really swapping at the same time, against the same liquidity, or through the same route. The price they get is the price for their specific trade at that microsecond. For a full breakdown of all the costs that can differ between swaps, read the hub page What a crypto swap actually costs.

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