Slippage Explained: Why Your Fill Price Isn't Always the Price You Clicked

You click buy on EURUSD at 1.1642. The confirmation shows a fill at 1.1644. Two pips vanished between the click and the confirmation — nobody stole them, no platform bug fired. That gap has a name: slippage. It is one of the most misunderstood parts of retail execution, and one of the most important to understand before trading around a scheduled release like the US Core PCE print due Wednesday at 08:30 GMT+3.

This piece walks through what slippage actually is, why it happens, when it tends to be worst, and how to think about it as a cost of doing business rather than a personal grievance against the market.

What Slippage Actually Is

Slippage is the difference between the price displayed when you submitted an order and the price at which it was executed. It can be negative (you paid more than you expected on a buy, or received less on a sell) or positive (you got a better price than requested). Most traders only notice the negative kind, but positive slippage exists too — it is simply the same mechanic working in your favour.

It is important to separate slippage from spread. The spread is the difference between the best bid and the best offer at any given instant. Slippage is what happens after you press the button, when the market you saw a moment ago is no longer the market that is available to trade.

A useful mental model: the price on your screen is a photograph. Your order is you walking into the room the photograph was taken in. Between the shutter click and your arrival, people have moved.

Why It Happens — Latency, Liquidity, and Volatility

Three factors drive almost all slippage.

Latency. Every order travels a physical distance from your device to the venue where it is matched. Even a well-connected retail setup runs on the order of tens to a few hundred milliseconds round-trip. In quiet markets, prices barely move over that window. In fast markets, they can move several pips.

Liquidity at your price. A quoted price is only good for a certain volume. If you send a market order for a size larger than what is resting at the top of the book, part of your order fills at the next available price, then the next, and so on. This is sometimes called "walking the book." A one-lot EURUSD order rarely walks the book. A fifty-lot order into a thin session sometimes does.

Volatility. When the tape is moving fast — around an economic release, a central bank speech, or a geopolitical headline — bids and offers are being cancelled and replaced constantly. The price you clicked may have been withdrawn before your order arrived.

All three factors compound around scheduled events. This is why the same instrument, at the same broker, on the same account can slip half a pip on a Tuesday afternoon and five pips in the seconds after a CPI release.

A Worked Example (For Illustration)

Assume — purely for illustration — that you want to buy one standard lot of EURUSD. The screen shows 1.1642 / 1.1643. You click buy at the offer.

• Scenario A: quiet market. Your order arrives 80 milliseconds later. The offer is still 1.1643. You fill at 1.1643. Zero slippage.
• Scenario B: mid-session drift. By the time your order arrives, the offer has ticked up to 1.16435. You fill at 1.16435. Negative slippage of half a pip — roughly $5 on a standard lot.
• Scenario C: seconds after a data print. The pair is moving 15 pips in two seconds. Your order arrives, the 1.1643 offer is long gone, and the next available offer is 1.1651. You fill at 1.1651. Negative slippage of eight pips — roughly $80 on a standard lot.

None of these outcomes involves anyone doing anything wrong. They are the same order type meeting three different market states.

Positive slippage works the same way in reverse. If the offer drops to 1.16425 between click and fill, you buy cheaper than you intended.

How Order Type Changes Your Exposure to Slippage

A market order prioritises certainty of fill. You will be filled — the price is whatever the book offers when your order arrives. This is the order type most exposed to slippage.

A limit order prioritises certainty of price. It will only execute at your specified price or better. If the market gaps through your limit, you do not get filled at all. Zero slippage, but potentially zero trade.

A stop order becomes a market order once your trigger price is touched. This means stop orders inherit the slippage profile of market orders — and because stops are frequently triggered during fast moves, they are one of the most common sources of unexpected fills.

A stop-limit combines the two: it triggers at your stop level but then behaves as a limit. It protects against slippage but reintroduces the risk of no fill.

There is no free lunch here. Every choice trades one risk for another.

Slippage Around Scheduled Events

The economic calendar this week is a useful case study. Wednesday 26 August at 08:30 GMT+3 brings the US Core PCE Price Index (m/m), forecast 0.2% versus 0.1% prior, alongside Prelim GDP q/q at 1.5%. Later the same day, Australian CPI y/y is due at 21:30 GMT+3 with a forecast of 3.3% versus 3.8% prior.

In the seconds around each release, expect the following:

• Spreads on the affected pairs typically widen as market makers pull quotes
• Depth at the top of the book thins
• Latency-sensitive orders are more likely to experience negative slippage
• Stop orders resting near recent highs and lows are more likely to trigger

None of this is unusual — it is a normal feature of price discovery. Traders who deal with events routinely tend to either size down, switch to limit orders, or step aside for the first minute or two.

One Takeaway

Slippage is not a fault in the system. It is the price of using market orders in a market that keeps moving after you have made your decision. Treating it as a cost rather than a surprise — budgeting for it the same way you budget for spread and commission — is the shift that separates traders who complain about fills from traders who plan around them.

If you want to see how our execution behaves around Wednesday's PCE print, the calendar is on our platform and our support desk is happy to walk through order-type choices before the release.