Slippage is the difference between the price expected when an order is placed and the price at which that order is actually filled.
That sounds technical, but the idea is simple. Markets move. Available prices can change in the short time between sending an order and having that order executed. When that happens, the final fill may differ from the price first seen on screen.
This is one of the most commonly misunderstood parts of trading. Many people assume that any difference between the expected price and the actual fill must mean something has gone wrong. In reality, slippage is often a normal feature of live markets, especially when prices are moving quickly or available liquidity is changing. Market structure sources consistently show that execution quality is influenced by market width, depth, and the amount of liquidity available at the time of execution.
Quick explanation
If the visible price is 1.2050 when an order is placed, but the order is filled at 1.2052, that difference is slippage.
The same can work in the other direction too. If the order is filled at 1.2048 instead, that is also slippage. In other words, slippage is not automatically negative. It simply means the final execution price differed from the expected one.
The key point is that market prices are not static. Between click and fill, the market may move, the available size at a given price may be reduced, or the order may need to interact with different levels of available liquidity.
Why slippage happens
Slippage usually comes down to one or more of the following factors.
Price movement during execution
Markets can move in very short time windows. If the price changes before the order is matched, the execution may take place at a different level.
Available liquidity at the quoted price
A quoted price may only have limited size available behind it. If an order is larger than that available amount, parts of the order may be filled at the next price level or levels.
Volatility
Around major news releases, market open and close periods, or sudden risk events, prices can move faster and gaps between available prices can widen. FINRA’s guidance on volatile conditions notes that stop orders can convert into market orders and execute at prices very different from the stop price when markets move quickly.
Thin market conditions
Some times of day naturally have less depth and lighter participation. When markets are thin, even modest order flow can have a larger impact on fill quality.
How liquidity and volatility affect fills
Liquidity and volatility are two of the biggest drivers of slippage.
Liquidity refers to how much buying and selling interest is available at or near the current price. Deeper markets tend to absorb orders more smoothly. Thinner markets tend to move more easily when new orders arrive. CME material describes market quality in terms of both width, the bid-ask spread, and depth, the quantity available at price levels, which directly affects potential slippage.
Volatility refers to how quickly prices are moving. In fast conditions, the market seen on screen a moment ago may no longer be available by the time an order reaches execution.
This is why slippage often becomes more noticeable:
- around economic data releases
- during central bank announcements
- after major geopolitical headlines
- near market open or rollover periods
- in instruments with lighter depth
Is slippage always negative?
No.
This is an important point because most discussions of slippage focus only on worse fills. But slippage simply means the execution price differed from the expected price. That difference can be less favourable or more favourable depending on how the market moved.
The better way to understand slippage is not as a one-direction penalty, but as a sign that live prices changed during the execution process.
What slippage does and does not tell you
Slippage does tell you that there was a difference between expected price and actual fill.
Slippage does not automatically tell you:
- that something improper happened
- that a broker “caused” the market movement
- that execution quality is always poor
- that the same outcome would happen in every market condition
Good trust-and-process content should make this distinction carefully. A single fill needs to be understood in context: market speed, size, liquidity, price path, and time of day all matter.
Common situations where slippage is more likely
Major data releases
When inflation, employment, or central bank announcements hit the market, prices can move quickly and available liquidity can shift rapidly.
Market opens and session changes
The transition between trading sessions can produce uneven conditions, especially if participation changes suddenly.
Large order size relative to depth
If the order is larger than the liquidity available at the quoted price, the fill may need to move through multiple levels.
Fast-moving or thinly traded instruments
Where there is less depth, prices can move more sharply in response to new orders.
Common misunderstandings
“Slippage means the broker changed the price.”
Not necessarily. Slippage often reflects live market movement or changing liquidity during execution.
“If the price on screen was available, that is the price I should always get.”
Not always. What is visible on screen can change in live conditions before an order is filled.
“Slippage only happens in bad environments.”
No. It can happen in normal market conditions too, although it is usually more noticeable during fast or thin periods.
“Tight spreads mean no slippage.”
No. Spread and slippage are related to execution conditions, but they are not the same thing. A market can appear tight and still move during execution.
Frequently asked questions
What is slippage in simple terms?
It is the difference between the price expected when placing an order and the price actually received when the order is filled.
Does slippage only happen in volatile markets?
No. It is more noticeable in volatile markets, but it can occur whenever prices or liquidity change during execution.
Is slippage always negative?
No. It can be negative or positive.
Does slippage mean something is wrong?
Not on its own. It usually means live market conditions changed between order submission and fill.
What factors influence slippage most?
Liquidity, volatility, order size, time of day, and how quickly the market is moving.
How is slippage different from spread?
Spread is the difference between bid and ask. Slippage is the difference between expected price and actual fill.
Why does slippage matter?
Because it affects execution outcomes and helps explain why live fills can differ from the price first seen on screen.