Slippage & Commission Calculator

Slippage is the difference between the price you expected when you placed an order and the price at which the order actually executed. It occurs in every market — stocks, forex, futures and crypto — and is caused by fast-moving prices, thin liquidity, or large order sizes. For a buy order, filling at a higher price than expected is adverse (negative) slippage; for a sell order, filling at a lower price than expected is adverse. Favourable slippage is also possible: a buy can fill lower than expected in fast-falling markets.

Slippage is calculated as: Slippage % = ((Fill Price - Expected Price) / Expected Price) × 100. The dollar slippage cost is: |Fill Price - Expected Price| × Quantity. For example, if you expected to buy 100 shares at $50.00 but filled at $50.10, the slippage is $0.10 per share and $10 total. Whether $0.10 is adverse or favourable depends on trade side: for a buy, a higher fill is a cost; for a sell, a lower fill is a cost.

Commission is a fee explicitly charged by your broker for executing the trade — it is disclosed on your confirmation and is predictable. Slippage is an implicit cost caused by the difference between your intended price and your actual fill — it is unpredictable and can be zero or even negative (favourable). Both are real costs that eat into your returns: a trade that looks profitable before accounting for execution costs may be marginal or loss-making afterwards.

The three most common models are: (1) Percentage of trade value — you pay a fraction (e.g. 0.1%) of the total notional (fill price × quantity); common with full-service and international brokers. (2) Per-share or per-contract rate — a fixed charge per unit (e.g. $0.005 per share); common with US discount and direct-access brokers. (3) Flat fee per trade — a fixed amount regardless of size (e.g. $0 at zero-commission brokers, or $4.95 at some legacy brokers). Many brokers also apply a minimum commission per trade, which is relevant for small orders.

A round-trip cost is the total execution cost for both legs of a trade: the entry (buy) and the exit (sell). It includes the commission for both transactions plus any slippage on both sides. For a trader, this is the complete cost that must be recovered before the trade becomes profitable. For example, if entry slippage is $15, exit slippage is $15, and commission is $10 each way, the round-trip cost is $50.

The break-even move is the price distance (in currency per unit) that the trade must move in your favour just to recover all execution costs — slippage plus commission. It equals total execution cost divided by quantity. For example, if total costs are $50 on 100 shares, the break-even move is $0.50 per share. If the stock moves $0.50 in your direction after entry, you have covered your costs and are at zero profit before other expenses.

Algorithmic traders, particularly at high frequency, typically measure slippage in fractions of a basis point (0.001%) and operate on very thin margins — even 0.01% slippage can eliminate a strategy’s edge. Retail traders face wider bid-ask spreads and higher per-trade slippage in absolute terms, but execute far fewer trades per day, so individual trade slippage is more manageable. Both must include round-trip slippage in every strategy backtest; ignoring it is a common reason why backtests outperform live trading.

No. Favourable slippage occurs when you are filled at a better price than expected: a buy order fills below the expected price, or a sell order fills above it. This commonly happens during fast-moving markets when prices move in your favour between order submission and execution. However, favourable slippage is not systematic — on average, market impact and adverse price moves mean most traders experience net adverse slippage over many trades, particularly on larger orders.

The sign convention is based on which direction harms the trader. For a buy, you want to pay as little as possible, so paying MORE than expected (fill > expected) is adverse — the slippage is a cost. For a sell, you want to receive as much as possible, so receiving LESS than expected (fill < expected) is adverse — the slippage is also a cost. Both scenarios increase the total cost of the trade; both are adverse. This is why a fill price below the expected price is favourable for a buy but adverse for a sell.

Yes — ignoring slippage in a backtest is one of the most common causes of overstated backtest performance. Backtests typically assume fills at the quoted price; real execution always incurs some slippage. A simple approach is to add a conservative fixed slippage estimate (e.g. 0.05% per side) to every simulated trade. For strategies that trade at the open or on limit orders, a smaller estimate is reasonable; for market orders in less liquid instruments, a larger one is appropriate. Always test sensitivity to the slippage assumption.

Practical ways to reduce slippage include: using limit orders instead of market orders (limits cap your execution price, but carry non-fill risk); trading liquid instruments with tight bid-ask spreads; avoiding entries at market open when volatility and spread are typically highest; sizing positions so your order does not significantly move the market (institutional-scale market impact slippage); and routing orders through direct-access brokers that offer smart order routing across multiple venues.

The bid-ask spread and slippage are both transaction costs, but they arise differently. The bid-ask spread is the fixed, visible gap between the best price a buyer will pay (bid) and the best price a seller will accept (ask). When you send a market order, you immediately cross this gap and pay the spread — it is a known, predictable cost visible on the order book before you trade. Slippage is an additional, unpredictable cost that occurs when the price moves between the moment you submit an order and the moment it executes, causing a fill that is worse than the price you saw at submission. In fast or illiquid markets, both costs hit you on the same trade: you cross the spread, and then adverse price movement adds further slippage on top.

Acceptable slippage depends on the instrument and market conditions. As a rough guide: on liquid large-cap stocks or major forex pairs in normal sessions, round-trip slippage below 0.1–0.2% is typical and considered acceptable for most strategies; slippage consistently above 0.3% per round trip starts to erode the edge of all but the highest-win-rate systems. In less liquid instruments (small-cap stocks, exotic forex, thinly traded crypto) 0.5–1% per side is common. During news events or at the open, even liquid instruments can see multi-pip or multi-cent spikes. The key test is not a fixed number: compare your typical slippage against your strategy's average profit per trade and break-even move — if slippage regularly exceeds 20–30% of your average winner, execution costs are a meaningful drag worth addressing.