What is slippage around news?
Slippage is the difference between the price you expect at the moment you place an order and the price you actually get when the trade is filled. In the context of news, “around news” means the time window where market conditions can change quickly due to a scheduled information release (for example, an economic statistic). During that window, prices may move faster than your order can be matched and executed.
It helps to separate two ideas:
- Execution mechanics (stable): how orders are routed, queued, filled, and reported.
- Market/provider conditions (variable): changes in volatility, liquidity, and the bid–ask spread.
Because both change at once, the observed difference between expected and actual prices can come from multiple sources, not just one.
Mechanism worked example (with explicit assumptions)
Here is a transparent scenario. Numbers are illustrative and meant to show the calculation steps.
Assumptions
- You place a market order (an order that seeks immediate execution, not a specific price).
- At the instant of placement, the market shows bid = 1.1000 and ask = 1.1002.
- Your trade is a buy for 10,000 units.
- Your “expected price” is taken as the current ask at placement: 1.1002.
- During the news moment, the market moves quickly and your fill occurs at a worse price due to execution latency and changing liquidity.
- Your actual filled price is 1.1015.
Calculation
- Expected fill price: 1.1002
- Actual fill price: 1.1015
- Slippage (price difference): 1.1015 − 1.1002 = 0.0013
To express it in “pips” for a typical 4/5-decimal forex quote style:
- If 1 pip = 0.0001, then 0.0013 / 0.0001 = 13 pips.
Why the fill can be worse during news
In this scenario, the main contributors are:
- Quote-to-fill gap: the price changes between when you see the quote and when the order matches.
- Liquidity gaps: fewer offers at or near your expected price.
- Spread widening: the bid–ask range increases, so the nearest available price becomes less favorable.
Even if the market is moving “in your direction” on average, moment-to-moment matching can still produce a fill that is worse than the last visible quote.
Limitations and risks (material failure modes)
A worked example is useful, but it cannot guarantee the future because slippage around news is conditional. Common limitations include:
- Order type mismatch: The result depends strongly on whether you used a market order, a limit order, or another execution instruction. A limit order may avoid slippage but can lead to missed fills.
- Latency and routing effects: Time delays between order submission, routing, and execution can dominate the outcome.
- Partial fills: If an order is filled in pieces at different prices, “slippage” may need a weighted-average calculation rather than a single difference.
- Spread and liquidity dynamics: During news, the bid–ask spread can widen and available depth can shift, changing the prices at which fills occur.
- Expectation definition ambiguity: Different people define “expected price” differently (last quote, mid price, best bid/ask at placement, or an internal reference). Your slippage number will change with that definition.
How to verify slippage around news independently
To verify and explain slippage for a real event, you can use a disciplined approach:
- Collect execution records: order submission time, fill time(s), filled price(s), and order type.
- Define your reference price clearly: for example, best ask for a buy at submission, or mid price if you want a symmetric measure.
- Calculate slippage consistently: use the same reference price and, if there are multiple fills, use a weighted-average actual price.
- Separate phases: compare the quote behavior right before placement with the fill window, to see whether the issue is spread widening, liquidity gaps, or delayed execution.
A useful next question is: Was the slippage primarily caused by rapid price movement (market), or by delays in execution and matching (mechanics)? The logs help you distinguish those explanations.