Slippage in Forex: Why Your Fill Differs From the Screen

You click buy at one price and the confirmation shows another. The trade is already open, the difference is small, and the usual explanation offered is that the market moved. That explanation is true and almost useless, because it does not tell you which of several different things just happened.

Slippage is one specific mechanism among four that make a fill differ from the number on screen, and each has a different cause, a different remedy and a different implication for whether your broker did anything wrong. This guide separates them, explains the platform setting that decides whether an order slips or is refused, and shows how to measure your own slippage instead of guessing at it.

What Slippage Actually Is

Slippage is the difference between the price an order was requested at and the price it was actually filled at. The order executed; only the price changed.

That last point separates it from everything else on this page. With slippage you hold a position, and the question is what it cost you. With a requote or a rejection you hold nothing, and the question is why. Where the request was passed onward to a liquidity provider, why a trade request is rejected comes down to the checks run inside the last look window.

The mechanism is straightforward. A market order asks to trade at the best price currently available, and between the moment your platform sends the request and the moment a counterparty accepts it, the best available price can change. The order is filled against whatever is there when it arrives.

Slippage, Spread Widening, Requotes and Gaps Are Four Different Things

Most explanations treat these as one topic called “the price moved”. They are four distinct events, and a trader who cannot tell them apart will misdiagnose their own fills and blame the wrong thing.

The practical distinction is between the two that leave you holding something and the two that do not. Spread widening and requotes are decision points where you can still walk away; slippage and gaps are outcomes reported to you after the fact. Separate from all four, which side of the quote triggers a stop decides whether the level drawn on your chart was ever the one being measured.

Gapping deserves particular attention because it is the one that defeats a stop-loss. If no price traded between your stop level and the reopening price, there was nothing at your level to trade against, and the fill happens wherever the market resumed. The same absence of tradable prices is why a stop out during a gap can close positions well below the level that triggered it.

Why a Fill Differs From the Price on Screen

Three conditions produce most of the difference, and they compound rather than substitute for one another.

The first is latency. The quote on your screen has already travelled to you, and your order has to travel back. On a fast-moving instrument the price at the far end is not the price you saw.

The second is available volume at the top of the book. A quote is good for a certain size, so an order larger than the volume resting at the best price fills the remainder at the next levels. That is why a bigger order can slip when a smaller one on the same instrument does not.

The third is thin liquidity. Around scheduled data releases, at market opens, and in the hours when few participants are active, the depth behind the quote is smaller, so the same order consumes more of it. None of these implies misconduct; they are properties of trading against a moving book.

The first of those conditions is what an attempt at latency arbitrage tries to trade against from the other side, which is also why it does not survive a retail connection.

Positive Slippage and Why Avoiding Slippage Is the Wrong Goal

Slippage runs in both directions. If the price moves in your favour between request and execution, the order fills better than you asked, which is usually called positive slippage.

This matters because almost every guide on the topic frames it as a problem to eliminate. On a market order it cannot be eliminated, because you have asked to trade at whatever price is available and that is exactly what you received.

What is controllable is different: the type of order you send, and the tolerance you attach to it. A limit order will not slip against you at all, because it will not fill above your specified price. The trade-off is that it may not fill.

So the honest framing is a choice between two certainties. A market order guarantees execution at an uncertain price; a limit order guarantees a price with uncertain execution. Slippage is the cost of choosing the first, not evidence that you chose wrongly.

The Slippage Tolerance Setting That Actually Controls It

There is a platform-level control for this, and it is missing from most explanations of the topic.

MetaTrader exposes a Deviation field in the order window. MetaQuotes documentation describes deviation as the difference between the order execution price and the specified price to which a trader agrees. If the price moves within that allowance, the order executes at the new price without a prompt. None of that applies where the order never reached the market: an order refused rather than filled is a different event with a different cause.

If it moves further, the behaviour depends on the execution mode your account uses, and this is the part that is routinely misunderstood.

Under Instant Execution the server can refuse the order and return new prices for you to accept or reject, which is precisely what a requote is. Under Market Execution the broker determines the execution price without that exchange, so there is no requote step and the deviation allowance does not hold the order back.

The consequence is worth stating plainly: setting a small deviation does not cap your slippage on an account that executes at market. It only changes behaviour where a requote is possible in the first place. Which mode applies is a property of your account, and it is stated in the contract specifications rather than chosen by you.

A wider deviation makes a requote less likely and a filled-but-slipped order more likely. A narrow one does the reverse where the mode allows it. Neither setting makes the market move less.

How Stop-Loss and Guaranteed Stop Orders Behave

A standard stop-loss is not a price guarantee. It is an instruction that becomes a market order once the trigger level trades, and from that moment it carries the same exposure to slippage as any other market order.

This is why a stop can be filled well away from its level during a fast move or over a weekend gap, and why it limits the intended size of a loss rather than fixing it. If you place stops from a volatility measure, setting a stop loss with ATR gives the distance, not the fill.

A guaranteed stop is a different instrument. CMC Markets states on its own platform page that a guaranteed stop-loss order closes the position at the price specified regardless of market volatility or gapping, and that the premium charged for it is refunded if the order is not triggered.

That is the only mechanism here that removes gap risk rather than reducing it, and it is charged for. Availability, premium size and covered instruments are set by each broker, so they belong in your own broker’s terms. This sits alongside the other decisions covered in forex risk management.

How to Measure Your Own Slippage

Most traders discuss slippage from impressions formed after the trades that annoyed them. Your trade history contains the actual numbers, which makes this measurable.

The method is mechanical. For each filled order, record the price you requested and the price you received, and take the difference in pips with its sign preserved so that improvements stay positive and worsened fills stay negative.

Keeping the sign is the step that changes the conclusion. An average that discards positive slippage will always show a cost, because you have removed half the distribution before averaging it.

Then group the results, because the average across all trades hides the pattern. Two groupings carry most of the information: by hour of the session, and by whether the order was placed within a few minutes of a scheduled economic release.

What you are looking for is not the overall average but the tail. A handful of large negative fills concentrated in one session hour or around one recurring event is an execution problem you can schedule around. An even scatter of small differences in both directions is ordinary market behaviour and not worth acting on.

A demo account is not a reliable source for this measurement, because demo servers do not always reproduce the fill behaviour of a live account.

When Slippage Matters and When It Does Not

Slippage is a fixed-size cost per trade, so its importance depends entirely on how it compares with the size of the move you are trying to capture.

Consider a hypothetical to make the proportion visible. Suppose a strategy targets fifteen pips and a fill differs by one and a half pips. That is a tenth of the target, before how the spread works is even taken into account. Apply the same one and a half pips to a strategy targeting three hundred pips and it is a rounding error.

This is why the topic is decisive for scalping and for trading around scheduled news, where targets are short and liquidity is thinnest at exactly the moment orders are sent. It is close to irrelevant for positions held over days with stops measured in hundreds of pips.

Frequency compounds this. A trader placing many orders a day meets the distribution far more often than one placing a few a month, so the same per-trade difference accumulates into a materially different annual figure.

Who should stop worrying about it: anyone whose stop distances are wide, whose holding periods are long, and whose measured history shows small differences in both directions. Adjusting a strategy to chase a cost that small will do more damage than the cost.

Frequently Asked Questions

Is slippage the same as a wider spread?

No. Spread widening changes the quote before you trade, so you can see it and decline. Slippage happens to an order you already sent, and you learn about it from the confirmation. One is a visible cost of entering; the other is a difference between the price requested and the price received.

Can slippage work in your favour?

Yes. If the price moves in your direction between the request and the execution, the order fills at a better price than asked, which is normally called positive slippage. Any measurement that counts only unfavourable fills will overstate the cost, because it discards half of the distribution.

Does a stop-loss order protect against slippage?

No. A standard stop-loss becomes a market order once its level trades, so it is filled at the next available price like any other market order. It limits the intended size of a loss rather than fixing it, which is why fills can land well past the level during fast moves and weekend gaps.

What is a slippage tolerance or maximum deviation setting?

It is a field in the order window setting how far the execution price may differ from the requested price before the order is not simply filled. MetaQuotes documentation defines deviation as the difference to which the trader agrees. It changes behaviour where a requote is possible, and does not cap slippage on accounts executing at market.

Is slippage a sign of a bad broker?

Not by itself. Slippage in both directions, concentrated in fast markets and thin hours, is ordinary. What is worth examining is a pattern that runs one way only, or large differences that appear in calm conditions. Measure your own fills before drawing a conclusion, and read the broker’s order execution policy for how it says orders are handled.