What is slippage in prop trading?
What slippage is, why it cannot be read off a price feed, and how PropSpread handles it: as a clearly labeled assumption next to measured spreads, never mixed into them.
PropSpread ResearchPublished Aug 13, 20264 min read
Slippage is the difference between the price you asked for and the price you were filled at. You click a buy at one number, the order reaches the server a few milliseconds later, and the market has moved a fraction in between. The fill lands on the price that existed when the order arrived, not the one you saw. That gap, positive or negative, is slippage.
Why slippage matters inside an evaluation
Like the spread, slippage is a cost paid at the fill rather than a line on a statement, and inside a prop firm evaluation it spends the same two scarce resources: distance to the profit target and headroom under the drawdown limit. A strategy that enters on fast moves, around news or at session opens will pay more of it than one that enters in quiet conditions, because slippage grows exactly when prices move faster than orders travel.
- Market orders pay slippage in fast markets; limit orders trade it for the risk of not being filled.
- News releases and session opens are where fills drift furthest from the quoted price.
- Stop losses are market orders once triggered, so exits can slip exactly when it hurts most.
Why slippage cannot be read off a price feed
A spread is visible in the quote itself: the distance between bid and ask exists whether or not anyone trades. Slippage only exists at the moment of a real fill, on a real order, at a real size. Measuring it honestly would require placing actual orders at every firm continuously. A price feed alone cannot produce that number, and any site that publishes a precise slippage figure without trading real orders is estimating, whether it says so or not.
How PropSpread handles it
PropSpread keeps the two kinds of numbers apart. Spreads are measured from connected feeds and carry sample counts. Slippage appears only as a clearly labeled assumption in the trade cost simulator, stated in dollars per lot, shown separately from the measured components and excluded from planning calculators where it would blur the arithmetic. When you see a total that includes slippage, the assumption behind it is printed next to the number.
The practical takeaway is the same one the spread guide ends on: plan with the costs you can see, leave margin for the ones you cannot, and treat any single number that claims to capture both as a starting point rather than a fact.
The costs you can see, live
The module below shows the measurable half of the invoice for EUR/USD at the tracked firms: the currently sampled spread converted to dollars per one-lot round turn, plus each firm's configured commission. Slippage is deliberately absent here, because it belongs to your orders, not to a feed.
Estimated cost of one EUR/USD round turn at 1 lot
Source: PropSpread market monitoring. Full sampling, normalization and ranking rules are on the methodology page.
Frequently asked
Is slippage always a cost?
No. A fill can land on a better price than requested, which is positive slippage. In fast markets the drift tends to run against market orders more often than for them, which is why planning treats it as a cost with margin rather than a coin flip.
Can slippage be avoided completely?
Not on market orders in moving markets. Limit orders remove price surprise but add fill uncertainty. The realistic goal is to control when you pay it: calm conditions, sensible sizes, and no market entries into scheduled news unless the strategy prices that in.
Why does the simulator state slippage as an assumption?
Because an honest site cannot measure your fills without placing your orders. The simulator prints the assumption it uses in dollars per lot, keeps it separate from measured spread and commission, and lets you judge the scenario with the label in view.
Editorial policy
PropSpread Research publishes sampled data with its methodology and data-source labels attached, keeps editorial judgment separate from measurements, and labels commercial relationships where they exist. Corrections are welcome via the contact page.
This tool provides an indicative comparison of spreads and estimated execution costs based on periodic snapshots from connected data feeds and normalized trade assumptions. Displayed values are not tradable quotes and may differ from prices available on any provider's live accounts. Spreads vary by account type, server, liquidity conditions, and time of day. Competitor names and marks belong to their respective owners; no affiliation or endorsement is implied. The "Average Prop Firm" benchmark is a computed composite of sampled competitor feeds, not the published pricing of any specific firm. Cost estimates use a normalized trade scenario and do not constitute financial advice or a prediction of trading results.