Slippage

Slippage happens most on market orders (which take whatever price is available) and on thinly-traded pairs, where a single order can move through several price levels before it's fully filled.

For example, expecting a fill at $60,000 but getting an average fill of $60,150 on a $50,000 order means $150 of slippage, or 0.25% of the trade — on top of whatever the exchange's stated trading fee is.

A common mistake is comparing exchanges purely by their advertised trading fee and ignoring slippage. A 'low-fee' exchange with a wide spread and a thin order book can end up costing more per trade than a slightly higher-fee exchange with deep liquidity.