™Planning a buy at $50 but filling at $50.10 on 100 shares adds $10 of execution cost relative to the assumed price.
Orders & Market Structure
Slippage
The difference between an expected transaction price and the actual execution price.
Plain-English context
Put the definition to work.
Choose a consistent reference price and sign convention. Adding estimated slippage to already actual fills can double count it.
Further reading and verification. Examples are hypothetical, not current quotes or recommendations. Product terms, tax treatment and market rules can change. FINRA — order types and execution