Slippage

Slippage is the difference between the price you expected to trade at and the price you actually got. You plan to buy at $50.00, the order fills at $50.03, and the three cents per share is slippage. It applies to every kind of exit as well, and it is often largest on a stop-loss, the order you most want to fill at its price.

Slippage is a trading cost, in the same family as commissions and the bid-ask spread, but it is easier to miss because it never appears as a line item on a statement. It hides inside the fill price. Over hundreds of trades it can be the difference between a strategy that works and one that does not.

How Slippage Happens

Most slippage comes from the way orders execute. The SEC's investor guide states the core of it: a market order "guarantees that the order will be executed, but does not guarantee the execution price" (Investor.gov, Types of Orders). Your order takes whatever price is available when it reaches the market.

Stop orders work the same way once triggered. In the SEC's words, "the stop price is not the guaranteed execution price for a stop order," and the fill "can deviate significantly from the stop price due to the prices of available liquidity" (SEC investor bulletin on stop orders). That is why a stop-loss can fill below its level.

The usual sources:

• Fast markets. Price moves between the moment you click and the moment the order fills, most often around news, the open, and the close.
• Gaps. If price opens below your stop, the stop fills at the first available price, which can be far past your level.
• Thin liquidity. In a lightly traded stock, an illiquid option, or a small crypto token, the next available price can be several ticks away.
• Order size. If your order is larger than the size quoted at the best price, it fills through several price levels. This is called market impact.
• The spread. A market buy fills at the ask, not the last trade or the midpoint, so part of what traders call slippage is simply paying the spread.

How to Measure Slippage

The calculation is simple once you record the price you intended:

Buy slippage = fill price − expected price Sell slippage = expected price − fill price

A positive number is a cost. Multiply by size to get dollars. Divide by your stop distance to get it in R-multiples, which is the version that tells you how much it matters.

Example. You buy 500 shares with a planned entry of $50.00 and a stop at $47.20, so 1R is $2.80 per share. The entry fills at $50.03 and, a few days later, the stop fills at $47.12 in a fast move.

The planned loss was 1R, $1,400. The actual loss was $1,455, or about 1.04R. One trade like that is noise. The same thing on every losing trade raises your average loss, and that feeds into expectancy and profit factor.

Why Slippage Hurts Tight Stops Most

Slippage is roughly a fixed amount per share for a given market and order type. Your stop distance is not. So the same few cents are a tiny slice of a wide stop and a large slice of a tight one.

The chart takes a strategy that makes +0.20R per trade before costs and charges it two cents of slippage on the entry and two on the exit, four cents per round trip.

Nothing about the setup changes from row to row. With a $2.00 stop the edge barely notices the cost. With a 20-cent stop the entire edge goes to slippage, and with a 10-cent stop the strategy loses money. This is why scalping and other tight-stop styles live or die on execution, and why a backtest that assumes perfect fills tends to flatter them most.

Slippage vs. Spread vs. Commission

All three come out of the same trade. A complete picture of a strategy's costs needs all of them, and slippage is the one only you can measure, because only you know the price you meant to get.

How to Reduce Slippage

• Use limit orders where a missed fill is acceptable. A limit order cannot fill worse than its price, which is why take-profit exits are usually limits. The cost is that some trades will not fill.
• Avoid the most volatile minutes unless your strategy depends on them. The open, the close, and scheduled news are where fills slip most.
• Size to the market. Keep orders small relative to the size quoted at the best price and the instrument's typical volume.
• Prefer a wider stop with a smaller position. For the same dollar risk, a wider stop makes each cent of slippage a smaller share of 1R. Position sizing keeps the dollar risk the same.
• Budget for it in backtests. Charge a realistic amount per side, based on your own fills, before deciding a strategy has an edge.

Key Takeaways

• Slippage is the difference between the price you expected and the price you got, and it usually works against you.
• Market orders and triggered stop orders guarantee a fill, not a price, so they are where slippage lives.
• Measure it in R by dividing slippage per share by your stop distance.
• A few cents of slippage can erase the edge of a tight-stop strategy that a wide-stop strategy would barely notice.
• You can only measure slippage if you record the price you intended before the trade.

Common Mistakes

Not recording the intended price. Without the planned entry and stop, there is nothing to compare the fill against, and slippage disappears into "the market moved."

Backtesting at chart prices. Assuming every order fills at the exact signal price overstates results, most of all for strategies with small targets and tight stops.

Treating a bad stop fill as bad luck. One gap through a stop is bad luck. A pattern of stop fills a few cents worse than planned is a cost that belongs in your numbers.

Chasing entries with market orders. Hitting the ask on a stock that is already running is often where the largest entry slippage comes from.

Ignoring it because it looks small. Two cents feels like nothing next to a $50 stock. Next to a 20-cent stop, it is a tenth of your risk.

How JournalX Tracks Slippage

Measuring slippage needs two prices: the one you planned and the one you got. JournalX records the first through pre-trade planning, where you set your entry, stop, and target before the trade, and pulls the second from your broker sync or import. Comparing the two shows how far your real fills land from the plan, and whether a stop-out cost you 1R or 1.1R. That is the same comparison the guide on how to calculate expectancy works through by hand, and it is why the planned versus actual entry price is worth logging on every trade. Filter by setup, symbol, or session and you can see where execution costs are eating into the edge.