Bid-Ask Spread
The Formal Definition
The numerical difference between the highest price a buyer is willing to pay (the Bid) and the lowest price a seller is willing to accept (the Ask) for an asset.
Spread = Ask Price - Bid Price
Cole Barrett's Reality Check
The Unvarnished Bottom Line"The spread is Wall Street's private toll booth. When an app advertises '$0 commission', this is where they scalp your trade. If you buy at an Ask of $100.05 when the Bid is $100.00, you are down -$0.05 the microsecond the order clears. Over a year of active trading, wide spreads cost far more than old-school flat commissions."
Interactive Simulator: Test the Math
Real-World Example: Scenario Breakdown
Examining the real numbers for: Apple Inc. (AAPL) @ $200 — 500 Shares ($100k Order)
| Execution Metric | Direct Market Access (IBKR Pro) | Zero-Commission PFOF App |
|---|---|---|
| Fee / Rate | $2.50 ($0.005/sh) | $0.00 (Free) |
| Spread / Buffer | 1¢ ($200.00 / $200.01) | 6¢ ($199.98 / $200.04) |
| Execution / Status | $200.01 | $200.04 |
| Total Cost / Result | Saved $12.50 vs retail | Lost $12.50 to spread markup |
How Brokers Weaponize This Term
Brokers sell retail order flow to quantitative market makers under Payment for Order Flow (PFOF). The market maker widens the spread by fractions of a cent, fills the order at a worse price, and splits the arbitrage with the broker. You get a '$0 commission' receipt while overpaying on the asset.
Broker Evaluation Matrix
Cole Approves
Interactive Brokers: SmartRouting Direct Market Access (DMA) with verified NBBO price improvement.
Read Audit →Cole Flags / Avoids
Standard PFOF Brokerages: Wide internal spreads and zero routing transparency.
View Trap Details →Frequently Asked Questions
Who keeps the bid-ask spread?
Market makers and liquidity providers keep the spread as compensation for facilitating instant trade execution.
How do I minimize spread drag?
Use Limit Orders instead of Market Orders, trade during peak market liquidity, and use brokers with Direct Market Access (DMA).