What This Calculator Measures
Every stock trade carries two layers of cost: explicit costs (commissions, exchange fees, SEC fees) that appear on your brokerage confirmation, and implicit costs (spread and slippage) that are embedded in the prices you receive. The explicit layer is visible; the implicit layer is often larger and harder to see.
This tool estimates both layers so you can compare brokers, validate a strategy's cost assumptions, and understand the minimum price move a trade needs to break even before any gross profit begins. All calculation happens locally in your browser — no prices, quantities, or results are sent anywhere.
Use Plan a Trade to estimate costs before you order. Use Review a Fill to analyze actual fills against a benchmark after execution. Results are estimates based on your inputs, not quotes or predictions of market behavior.
| Output | Definition | How to read it |
|---|---|---|
| Quoted spread | Ask minus bid | Top-of-book friction; tighter is cheaper |
| Weighted average fill | Quantity-weighted average of actual fill prices | True average cost when fills occur at multiple prices |
| Signed slippage | Side-adjusted fill vs benchmark in bps | Positive = unfavorable; negative = favorable vs benchmark |
| Effective spread | 2 × (fill − midpoint) / midpoint × 10,000 bps | Round-trip cost measure relative to midpoint |
| Explicit cost | Commission + entered fees | Shown separately from implicit (spread/slippage) cost |
| Total cost | Explicit + implicit costs in dollars | Full round-up of entry friction |
| Break-even move | Total cost / (quantity × fill price) × 10,000 bps | Minimum favorable move before the trade earns any gross profit |
Execution Cost Calculator
Results are estimates only. Actual costs depend on fill venue, order type, market conditions, and broker arrangement. Not investment advice.
Frequently Asked Questions
Does the calculator predict my fill?
No. It estimates outcomes from assumptions you enter (Plan mode) or analyzes actual fills you supply (Review mode). It does not predict hidden liquidity, queue position, future volatility, or whether an order will execute. Quotes can change before an order reaches a market.
What benchmark should I use?
Use the reference most aligned with your objective. NBBO Midpoint is the most common TCA benchmark and reflects the fair market price at order arrival. Arrival Ask or Arrival Bid suit strategies measured against the side they trade through — for example, a buy benchmarked to the ask shows how much price improvement (negative slippage) you captured. VWAP is appropriate when your execution objective is volume-weighted participation. The benchmark choice affects the sign and magnitude of slippage but not the weighted average fill price or explicit cost.
Why can slippage be negative?
Under the signed convention used here, negative slippage means the fill was favorable versus the selected benchmark — you bought below benchmark or sold above benchmark. The results label this "favorable" rather than "profit," because you still carry explicit costs and subsequent market movement determines the trade outcome. Negative slippage vs midpoint benchmark is called price improvement.
Does total cost include taxes?
No. Tax treatment depends on your account type, holding period, jurisdiction, and other factors that are account-specific. The calculator covers explicit brokerage costs (commission and entered fees) and implicit costs (spread and slippage). Financing costs, borrow costs for short sales, and corporate action effects are also excluded.
Can I enter multiple fills?
Yes. Review mode supports any number of fill rows. Click Add Fill Row to add rows, each with a fill quantity and price. The calculator computes a quantity-weighted average fill. A simple (unweighted) mean of the prices would be incorrect when fill quantities differ — for example, 200 shares at $10.00 and 800 shares at $10.05 gives a weighted average of $10.04, not the unweighted $10.025.
Are my values saved?
No. All calculations run locally in your browser. No prices, quantities, or results are transmitted to a server, stored between sessions, or captured in analytics. Refresh or close the page and all values are cleared.
Related Reading
- Market Structure & Trade Execution — hub
- Bid-Ask Spread & Liquidity — understand the inputs
- Slippage & Market Impact — interpret slippage results
- Order Routing & Execution Quality — apply execution-quality review
- Position Sizing & Risk Per Trade — apply cost to maximum loss
- Backtesting — use cost assumptions in strategy testing