Slippage occurs when the price at which an order actually executes differs from the price displayed or requested at the moment of submission. It happens because prices can move between the instant an order is sent and the instant it reaches the market, or because there simply isn't enough volume available at the requested price to fill the full order size.
Positive and Negative Slippage
Slippage isn't always unfavorable. Positive slippage fills an order at a better price than requested, which can happen in fast-moving markets in either direction. Negative slippage fills at a worse price. Over many trades in a genuinely fair execution environment, positive and negative slippage should roughly balance, though in volatile or thin conditions negative slippage tends to dominate.
The Role of Liquidity
Liquidity describes how much volume is available to trade at or near the current price. In deep, liquid markets like EUR/USD during London and New York overlap hours, large orders can typically be absorbed with minimal price impact. In thin markets — exotic pairs, low-cap stocks, or major pairs during the Asian session lull — the same order size can move the price noticeably, producing more slippage.
When Slippage Is Worst
- ▸Around high-impact news releases, when liquidity providers widen or pull quotes entirely for a short window.
- ▸During gaps between the Friday close and Sunday/Monday open, especially after weekend news.
- ▸In thinly traded exotic pairs or small-cap instruments at any time of day.
- ▸During flash-crash-style events where liquidity briefly evaporates entirely.
A standard stop loss becomes a market order once triggered, meaning it fills at the next available price, not necessarily the exact stop price. In a fast-moving or gapping market this can mean a materially worse exit than planned. This is a structural feature of standard stop orders, not a broker malfunction.
Order Types and Slippage Exposure
| Order type | Slippage exposure | Trade-off |
|---|---|---|
| Market order | Full exposure to available liquidity | Guaranteed fill, uncertain price |
| Limit order | None beyond the set price | Certain price, uncertain fill |
| Stop order | Becomes a market order once triggered | Guarantees exit, price can slip |
Managing Slippage Risk
Traders can reduce slippage exposure by avoiding market orders directly at scheduled high-impact news, using limit orders where fill certainty is less important than price certainty, and choosing brokers with transparent execution reporting. No method eliminates slippage entirely — it is a structural feature of real markets, not a flaw to be engineered away.
Illustrative example
Suppose a trader places a market buy order expecting a fill at 1.2000 during a major news spike, but the order actually fills at 1.2015 because liquidity briefly evaporated. This illustrative 15-pip slippage is an extreme but realistic outcome around unscheduled volatility spikes, and underscores why position sizing should account for worse-than-expected fills during high-volatility windows.