Reviewed September 10, 2026
Execution quality depends on more than the last traded price. Inspect spread, available depth, order size, price impact, fees, latency, and venue conditions together, and label every estimate as a snapshot.
At a glance
- Spread is the distance between the best ask and best bid.
- Depth is visible quantity at multiple price levels, not a promise that orders will remain.
- Slippage is the difference between expected and actual average execution price.
- A narrow spread does not guarantee low cost if the order consumes thin depth or pays high fees.
Step-by-step walkthrough
- Define the hypothetical order size and quote currency before reading the book.
- Record best bid, best ask, midpoint, and spread as both an amount and percentage when useful.
- Walk the order through successive levels to estimate a volume-weighted average price.
- Add venue fees and note that the estimate excludes latency, hidden liquidity, and cancellations.
- Compare the same order size across venues rather than comparing raw quantity totals.
- Repeat the snapshot at another time and report whether the result persisted.
Why the best quote is not the fill price
A market order that consumes multiple levels pays a size-dependent average.
| Signal | What it can mean | Important caveat |
|---|---|---|
| Best ask: $100.00 | The first available ask is quoted at $100. | Only the quantity at that level can fill there. |
| Next ask: $100.80 | Additional size moves up the visible book. | The level can change before execution. |
| Estimated average: $100.35 | The order-size-weighted estimate exceeds the best ask. | Fees, latency, and partial fills are excluded. |
Common mistakes and edge cases
- Using a single best quote to describe the cost of a large order.
- Comparing spread percentages without matching quote currency or asset price.
- Calling displayed depth “liquidity” without stating the order size and side.
- Ignoring fees, network costs, latency, market impact, and venue counterparty risk.
Reusable checklist
Checklist selections are temporary and are not transmitted or treated as a safety score.