Slippage Tolerance Sets a Swap’s Minimum Output

Slippage tolerance sets how many fewer tokens you will accept than a swap quote shows before the transaction fails. The interface starts with an estimated output, then applies your tolerance to calculate a minimum output. For an exact-input swap, a 1% tolerance means the transaction can complete if it returns at least 99% of the quoted amount. The router passes that minimum to the swap contract, which checks the actual output when the transaction executes.

A quote can change while a transaction waits to be included in a block. Other trades may move the pool price, or the swap itself may shift the price because the pool has limited liquidity. The tolerance is the boundary for accepting that change: if the output falls below the minimum, the swap reverts. Uniswap Labs’ support pages describe this minimum-output check and warn that a low tolerance can cause a swap to fail. The setting is separate from fees; for a breakdown of where they arise, see where Blackhole swap fees appear.

How is slippage tolerance different from price impact?

Price impact is the price movement caused by your own trade; slippage is the difference between the expected output and the output at execution. Uniswap Labs explains this distinction in its support guidance on price impact and price slippage. A large trade in a shallow pool can have high price impact before it is submitted. A smaller trade can still experience slippage if the market moves while it waits.

Think of the quoted output as a delivery estimate and the minimum output as the least you will accept. The estimate can change before arrival, but the minimum sets a firm limit. It does not predict the final price or promise that a transaction will succeed. It tells the contract when to stop instead of completing at a worse output.

What happens when tolerance is too low or too high?

A tolerance set below the price movement between quote and execution makes the swap revert. Setting it higher gives the transaction more room to complete, but permits a worse output. Uniswap Labs also notes that a high tolerance can let a user receive fewer tokens than the preview shows. On transparent blockchains, a pending swap with a wide minimum-output range may also be easier for a searcher to trade around, worsening the user’s execution.

• Low tolerance: tighter protection on output, with more risk that ordinary price movement makes the transaction fail.
• High tolerance: a better chance of completion, with permission to accept a larger shortfall.
• Minimum output: the practical figure to inspect in the swap details; it expresses the tolerance in tokens, not just as a percentage.
• Price impact: the estimated effect of your trade on the pool price, which is not the same as the tolerance you choose.

What should an occasional trader set?

For most occasional swaps, the interface’s suggested setting is a reasonable starting point because it is intended to account for the route and current conditions. Check the minimum-output figure before approving, especially for a thinly traded token or a large order relative to its pool. If the swap fails, first refresh the quote and inspect the route and liquidity. Raising tolerance blindly can make execution easier while allowing a materially worse result.

Tolerance is a trade-off between execution certainty and output protection. Keep it only as wide as needed for a swap you are willing to complete, and treat the minimum output as the limit that matters.