What Slippage Is and How It Differs From Commission
Slippage is the gap between expected fill and realized fill. Commission is a fixed per-trade charge. See how each is measured and why they show up separately.
By Imperial Analytics
Slippage and commission are both costs of trading, both reduce realized P&L, and both show up on the trader's account statement. They are not the same kind of cost. Commission is a fixed contractual charge per trade. Slippage is the gap between the price the trader expected to get filled at and the price they actually got filled at, measured in ticks and converted to dollars. The two are easy to confuse, and traders who treat them as one number underestimate one of them and lose the ability to manage either. This post defines both, names where each comes from, and walks through how a futures trader can pull the two apart in their own data.
By Imperial Analytics
What slippage actually is
Slippage is the difference between the price the trader intended to trade at and the price at which the order actually filled. On a market order, slippage is measured against the bid or ask the trader saw at the moment the order was sent. On a stop order or a stop-limit order, slippage is measured against the stop price. The number is expressed in ticks and converted to dollars using the contract's tick value, and it can be positive or negative depending on whether the fill was better or worse than the expected price.
The mechanics that produce slippage are mechanical, not behavioral. A market order on a thin book may sweep multiple price levels before it fills, and the realized fill is the volume-weighted average of those levels rather than the inside quote. A stop order that triggers in a fast tape converts to a market order at the moment the stop price trades, and the market order then fills at whatever liquidity is available at that instant. A stop-limit order avoids the worst-case slippage at the cost of accepting a no-fill outcome in fast markets.
Slippage is not a fee the broker charges. It is the cost of consuming liquidity at the price levels available when the order was sent. The broker passes the realized fill to the trader and does not separately invoice the slippage. The number is invisible to the trader who does not measure it; it shows up only as a smaller-than-expected winner or a larger-than-expected loser, attributed by default to "the market" rather than to the cost of execution.
Slippage has a sign. A fill at a better price than the trader expected is positive slippage. A fill at a worse price is negative slippage. In aggregate over many fills, slippage typically averages slightly negative for retail futures traders, because the moments when fast tape produces poor fills also tend to be the moments when the trader sends market or stop orders. Quiet conditions produce close-to-zero slippage; fast conditions produce most of it.
What commission actually is
Commission is the contractual per-trade fee the trader pays for routing and clearing the order. It is charged regardless of fill price, regardless of order type, and regardless of trade outcome. The amount is set by the broker and the exchange relationship, is published before the trade, and shows up as a separate line on the account statement. Commission is the cost of access, not the cost of liquidity.
The components of commission, in a typical retail futures account, are the broker's commission, the exchange fee, the clearing fee, and the regulatory fees that apply to the instrument. The exact composition varies by broker and by program, but the trader is charged a known total per side per contract, regardless of whether the trade made or lost money. Round-turn cost is the per-side cost times two, because both the entry and the exit are charged.
Commission is contractually deterministic. The trader knows what it will be before the order is sent. The number does not depend on book depth, on volatility, or on the trader's order type. It depends only on the contract traded, the size, and the trader's broker agreement. That predictability is what distinguishes commission from slippage on the trader's side of the table.
A separate line item, the exchange's market data fee, is sometimes lumped with commission in the trader's account statement. It is technically a fee for receiving data rather than a fee for trading, and it accrues whether or not the trader trades. For per-trade cost analysis the market data fee is treated as a fixed monthly cost rather than a per-trade cost, so it does not enter the slippage-versus-commission decomposition.
Data note
Numerical examples in this post are illustrative. Commission rates vary widely by broker and by program, and slippage statistics on a given instrument vary by session, by time of day, and by the trader's chosen order types. The trader should compute both numbers on their own fills before drawing conclusions about either, and should rely on the broker's published fee schedule for the contractual commission.
Where the two costs differ, line by line
Commission is contractual, deterministic, and depends only on size and contract. Slippage is mechanical, probabilistic, and depends on book depth, order type, and the moment of execution. Commission is paid the same way on every trade of the same size. Slippage is zero on some trades, small on most, and occasionally large; it has a distribution rather than a single value. The two numbers respond to different inputs and respond to those inputs in different ways.
The first difference is determinism. The trader who sends a one-lot market order on a given contract pays the same commission this morning as they will tomorrow afternoon, regardless of book state. The same trader's slippage on the same one-lot order will be small at the open, possibly larger in the first minute after an economic release, and possibly small again in a quiet midday session. Commission does not move with conditions; slippage does.
The second difference is order-type sensitivity. Commission charges the same on a market order, a limit order, and a stop order. Slippage is highest on market and stop orders, smaller on stop-limits when they fill, and zero on resting limit orders that fill at the limit price. A trader who shifts a percentage of their entries from market orders to limit orders can change the slippage line without changing the commission line at all.
The third difference is the route the cost takes to the trader's P&L. Commission shows up as a known deduction on the trade ticket. Slippage shows up as a small adjustment to the entry price and the exit price; the realized P&L is reduced because the entry was a tick worse than expected and the exit was a tick worse than expected, but no single line on the statement says "slippage cost on this trade." The cost is real and is hidden in the fills.
The fourth difference is what the trader can do about each. Commission is negotiated up front, sometimes annually, and varies in small steps once a broker relationship is established. Slippage is managed by order-type choice, by sizing, by time-of-day decisions, and by avoiding fast-tape conditions when the strategy does not require execution at that moment. The trader has more day-to-day control over slippage than over commission.
How to measure slippage on your own fills
Slippage is computed per fill by recording the intended price and the realized price and taking the signed tick difference, then converting to dollars using the contract's tick value. The aggregate slippage is the sum of those per-fill numbers over the window, and the per-trade average is the aggregate divided by the trade count. The honest version of the measurement records intended price at the moment the order was sent, not at the moment of fill, so the slippage number reflects execution rather than retrospective wishful thinking.
The intended price on a market order is the bid for a sell market and the ask for a buy market, taken at the moment the order is sent. The intended price on a stop order is the stop price itself. The intended price on a limit order that fills at the limit price is the limit price, which produces zero slippage. The intended price on a limit order that does not fill is undefined, and that trade is treated as a no-fill rather than a slippage event.
The realized price is the volume-weighted average fill price. On a one-lot order the realized price is the single fill price. On a multi-lot order that fills across more than one price level, the realized price is the volume-weighted average of the level fills, computed across all partial fills.
The signed difference, in ticks, is then realized minus intended for a buy and intended minus realized for a sell, so that a worse-than-expected fill always produces a negative number. Multiply by the contract's tick value, and the result is the dollar slippage on that fill.
Once the per-fill slippage is in the journal, the aggregate analysis follows the same shape as any other cost analysis. The trader can ask whether slippage clusters in specific times of day, in specific instruments, in specific order types, or in specific conditions. The pattern that emerges is what a slippage-reduction effort can target. Without the measurement, the cost is real and the targeting is impossible.
Why pulling the two apart matters
Treating commission and slippage as one number hides the part of the cost the trader can influence and the part the trader cannot. Commission is mostly fixed by the broker agreement, so its month-over-month change is small. Slippage can shift meaningfully with order-type choices and with time-of-day discipline. A trader who looks only at total trading cost will miss the slippage drift that signals a behavior change long before commission does.
A trader who runs a stable order-type mix should see a roughly stable per-trade slippage average month over month, with a few large outliers from fast-tape conditions. A drift in that average, from minus a quarter tick per trade to minus a full tick, is a signal that something has changed, either in the trader's execution choices, in the conditions of the instrument, or in the size relative to book depth. Commission does not move with any of those changes. The signal lives in the slippage line.
The same applies in the opposite direction. A trader who moves a portion of entries from market orders to limit orders should see the per-trade slippage average improve. That improvement is the realized result of the order-type change, and it is visible only when slippage is tracked separately. Bundled into a total-cost line, the improvement is washed out by the unchanged commission line.
The other half of the case for separating them is that the two costs respond to different decisions. Commission responds to a broker negotiation, a contract switch, or a volume tier change. Slippage responds to order-type choices, sizing, time-of-day discipline, and the trader's tolerance for missed fills. A trader who wants to lower trading cost has to know which dial controls which cost before turning either.
Frequently asked questions
Frequently asked questions
- q: Is slippage always negative? a: No. Slippage is the signed difference between the intended fill price and the realized fill price. A fill at a better price than expected produces positive slippage. In aggregate, retail futures slippage on market and stop orders tends to average slightly negative because the moments those orders are sent are often the moments of less favorable conditions, but individual fills can be positive.
- q: Does a limit order have slippage? a: A limit order that fills at the limit price has zero slippage by construction, because the realized price equals the intended price. A limit order that does not fill is a no-fill event rather than a slippage event. The trade-off the trader takes is between zero slippage with a fill-or-no-fill outcome on the limit, and certain execution with positive expected slippage on a market order.
- q: How does slippage relate to spread? a: The bid-ask spread is the difference between the inside bid and the inside ask at a given moment. A market order on a one-lot at the inside quote pays approximately half the spread as slippage relative to mid. Slippage is a more general concept than the spread because it accounts for fills that sweep multiple levels, for fast-tape execution, and for stop-order conversion mechanics.
- q: Should commission and slippage be combined for strategy analysis? a: For total realized P&L, both costs are subtracted from gross profit. For strategy improvement work, the two should be tracked separately, because they respond to different decisions. A trader who only has a combined cost line will struggle to attribute a change in cost to either the broker arrangement or the execution behavior.