What is slippage in crypto, and what does slippage tolerance do?

The price you saw, and the price you got

Uniswap Labs defines slippage as the gap between the price you were quoted and the final price of your trade.¹ FINRA describes the same gap in share markets: the price quoted to you may not match the price you pay.⁴

FINRA gives three reasons. Quotes may be delayed, trades take time, and in very volatile markets prices can swing in microseconds.⁴ Investor.gov says the same about market orders: the price you pay may not be the price you expected.⁵

Why it happens on a blockchain

A swap on a decentralised exchange (DEX) is a transaction, and it has to wait before it is added to a block.² The waiting area is called the mempool: transactions waiting to be processed.⁶

Uniswap's documentation says slippage covers the price changes that can happen while your transaction is pending.² Other people's trades can land first and move the price.^2,1

Uniswap Labs lists the usual causes: fast-moving markets, thin liquidity, big trades, and bots that trade around yours (Lesson 6).¹ Big trades and thin liquidity are the price impact problem from Lesson 3. Lesson 5 shows how it works in a pool.^1,2

Slippage tolerance

Uniswap Labs describes slippage tolerance as the largest price change you will accept between sending a swap and it being carried out.³ As of October 2025, its app called the setting "Max slippage".³

As of September 2025, Uniswap Labs said the app sets a tolerance, usually between 0.1% and 5%, based on gas fees and the size of the swap.¹ Uniswap's documentation for v2, an older version, gives 0.5% as its front end's default (Module 17).⁷

Under the hood, the tolerance becomes a minimum amount out. Uniswap's documentation says that if a swap would return fewer tokens than that minimum, the transaction reverts: it is cancelled, and nothing is swapped.²

Too tight, or too loose?

Uniswap Labs puts the trade-off plainly. A low tolerance keeps your price close to the quote but makes a failed swap more likely. A high tolerance makes the swap more likely to go through, but at a possibly worse price.¹

A failed swap is not free. Uniswap Labs says you still pay the network cost, also called gas.¹ Swaps can also carry a deadline: a time after which the swap is no longer valid and reverts.²

A wide tolerance has one more cost. Uniswap Labs says sandwich bots prey on wide slippage tolerances.⁸ Lesson 6 explains how.^8,9