You click sell on EURUSD at 1.0842 and the confirmation reads 1.0839. Nothing malfunctioned. The quote you clicked had already expired by the time the order left your machine, and when it reached a matching engine the best available bid was three pips lower. That gap between the intended price and the executed price is slippage, and it belongs in your cost model next to spread and commission rather than in the complaints folder.
The chain between the click and the fill
A market order passes through more hops than most traders picture. The platform sends it to the broker's server. A risk engine decides whether to internalise the order or pass it to a liquidity provider. If it routes out, the order reaches the LP, which checks that its own quote is still live, then fills, partially fills or rejects. Every hop costs milliseconds, and in a fast market the top of book can turn over several times inside fifty of them.
Two separate forces set the size of the gap. The first is how far price travelled during the round trip, which is a latency and volatility question. The second is how much size sits at the best price, which is a depth question. A 0.2 lot order in EURUSD during the London session normally clears at the top level. A 20 lot order eats through several levels, so the average fill is worse than the best quote even if the market never moved at all. Traders regularly blame latency for what is a position size problem.
Slippage runs in both directions
Positive slippage exists, and whether you receive it tells you more about a broker than any marketing page. When price ticks in your favour during the round trip, a symmetric execution model passes the better price through. Across a few hundred trades that produces a distribution with tails on both sides of zero. Asymmetric handling keeps the favourable ticks and passes on the unfavourable ones, and it shows up as a fill log in which nearly every deviation runs against the trader.
You cannot audit this from outside. You can audit it from your own trade history, which is one reason a per symbol slippage column earns its place in a trading journal. Record the price you requested, the price you got, the instrument, the size and the timestamp to the second. After two hundred trades the picture is no longer anecdotal.
Where it gets expensive
Slippage is not spread evenly across the week. It concentrates in a handful of predictable windows, and a trader who stays out of them removes most of the cost without touching anything else.
- The first seconds after a scheduled release. Market makers pull quotes ahead of the number, the book empties, and a market order can cross a gap rather than a spread. Payrolls and inflation prints are the usual suspects.
- The daily rollover around 17:00 New York, when liquidity providers change session and quotes thin out for a few minutes.
- The Sunday reopen, where the first tick can print well away from Friday's close and every resting stop triggers into that gap.
- Exotic and minor pairs at any hour, because the book behind them is a fraction of the depth behind EURUSD.
- Stop orders in a fast trend, since a stop becomes a market order the instant it triggers, in exactly the conditions that make market orders expensive.
Slippage is not a fee, so it never appears on a statement as a line item. It shows up as a strategy that backtests profitably and trades flat. If your model assumes fills at the signal price, it assumes something no live account receives.
Order type decides whether you can slip at all
Market orders accept whatever the book offers. Limit orders cannot fill worse than their stated price, which trades the risk of a bad fill for the risk of no fill, and in a runaway move that is often the better trade to make. Stop orders convert to market orders at the trigger, so a protective stop can and does slip past its level during a gap. Stop-limit orders cap the damage but leave the ugly possibility of an open losing position after price has jumped straight through the limit. Some brokers offer guaranteed stops on selected instruments for a premium, which is an insurance product rather than a free feature. The trade-offs are set out further in the guides to order types and stop placement.
Measuring your own number
Work in pips, not currency, so that sizes stay comparable. For each instrument, take the median deviation and the deviation at the ninetieth percentile, then split those figures by hour of the day. Two things usually appear. Entries clustered in the minute after a release carry a tail several times the size of the rest of the book of trades. And one or two instruments, typically an index or an exotic cross, carry median slippage that quietly doubles their effective spread.
What you do with that is a scheduling decision, not a technology one. Move the entry a few minutes later, switch the entry from market to limit, or drop the instrument. If the median deviation on your most traded setup is a meaningful fraction of the spread you pay, the fix is nearly always in the timing.
What the broker side controls
On the firm's side, the variables are the execution model, the number and quality of liquidity providers, whether the LPs apply last look, and the deviation tolerance configured per instrument. A max deviation setting rejects the order if the market has moved beyond a chosen number of points, which converts an unwanted fill into no fill. Firms operating under MiFID II also carry best execution obligations, which require them to take sufficient steps to obtain the best available result and to be able to demonstrate it. That is a documentation duty as much as a technology one, and it is the reason serious brokers keep tick level execution logs rather than summaries.
None of this makes slippage disappear. A trader who understands it prices it in and sizes accordingly. Leveraged trading carries a high risk of loss, and execution costs are one of the reasons live results diverge from tested ones.
"Nobody complains about the fills that come back better than the click. Keep the log for a month and you find out which kind of desk you are trading against."
— Alex Onta, Executive Director, SINGUARD
Key Takeaways
- Slippage comes from two separate causes, price movement during the round trip and insufficient depth at your size, and the fixes for them are different.
- A healthy fill log shows deviations on both sides of zero, so track the shape of the distribution rather than individual bad fills.
- Most of the cost lives in a few windows: the seconds after a release, the daily rollover and the Sunday reopen.
- Limit orders remove price risk at the cost of fill risk, while stops inherit market order behaviour at the worst possible moment.
Frequently Asked Questions
Is slippage a sign that my broker is cheating?
Not on its own. Slippage is a normal consequence of latency and book depth, and it appears on every execution model. The signal worth watching is the shape of the distribution. If your fills deviate in both directions across a few hundred trades, execution is behaving symmetrically. If almost every deviation is against you while the market clearly ticked in your favour on some of them, that is worth raising with the broker and checking against its best execution policy.
Which order types can slip?
Market orders can slip in either direction. Stop orders can slip because they become market orders the moment they trigger. Limit orders cannot fill worse than their stated price, so they trade the risk of a bad fill for the risk of no fill at all. Stop-limit orders cap the damage but can leave a losing position open if price jumps straight through the limit.
How do I reduce slippage without changing broker?
Trade sizes the top of book can absorb, avoid entering in the first seconds of a scheduled release, use a maximum deviation setting if your platform offers one, and prefer limit entries for setups that do not need immediate execution. Trading the deepest hours for your instrument, rather than the thin ones around the daily rollover, usually does more than any platform tweak.