NBBO

The National Best Bid and Offer (NBBO) is the best available bid price and best available ask price for a security across all exchanges at any given moment. For options, the NBBO represents the highest bid and lowest ask among all 16+ options exchanges. Brokers are generally required to fill customer orders at prices equal to or better than the NBBO, ensuring you get the best publicly available price.

Why It Matters

The NBBO is your benchmark for execution quality. When you place a market order, you should be filled at or near the NBBO. When you place a limit order at the midpoint of the NBBO, you are asking for a price between the best bid and best ask — a common strategy for getting a fair fill. Understanding the NBBO helps you avoid overpaying for options and set appropriate limit prices.

For options traders, the NBBO is especially important because options trade on multiple exchanges simultaneously. The bid on the CBOE might be $3.00 while the bid on the ISE is $3.05. The NBBO captures the best of both: the national best bid is $3.05. Your broker should route your order to get you at least this price, regardless of which exchange offers it.

How It Works

How the NBBO is calculated: Each options exchange continuously publishes its best bid and ask prices (quotes) for every listed contract. The NBBO processor takes the highest bid and lowest ask from across all exchanges and publishes the composite NBBO.

NBBO Bid = Highest bid across all exchanges NBBO Ask = Lowest ask across all exchanges

NBBO and order execution:

• Market orders: Must be filled at or better than the NBBO
• Limit orders: Filled at your limit price or better, as long as the NBBO allows
• Price improvement: Many retail orders are filled at prices better than the NBBO — between the bid and ask

The NBBO spread: The difference between the NBBO bid and ask is the spread. Tight spreads (penny-wide on liquid options like SPY) mean low trading costs. Wide spreads (dollars-wide on illiquid options) mean high trading costs.

NBBO in fast markets: During periods of high volatility, the NBBO can change rapidly — dozens of times per second. Your fill price depends on the NBBO at the exact moment your order is processed. This is why market orders during volatile periods can result in worse fills than expected (slippage).

NBBO limitations:

• Does not include dark pool or off-exchange prices
• Can be stale during fast-moving markets (the displayed price may be a fraction of a second old)
• Odd lot orders (less than 100 shares for stock) are not protected by NBBO rules
• The displayed NBBO may not reflect the actual available depth at those prices

Using the NBBO as a trader:

• Always use limit orders, set at or near the midpoint of the NBBO
• If the NBBO is $3.00 / $3.20, start with a limit at $3.10 and adjust if needed
• Be cautious of wide NBBO spreads — they indicate illiquidity
• Check the NBBO across multiple expirations and strikes to find the most liquid contracts

Quick Example

You want to buy the AAPL $180 call. The NBBO across all exchanges shows: bid $5.20, ask $5.30. The spread is $0.10 — very tight, indicating strong liquidity.

You place a limit order at $5.25 (the midpoint). A market maker fills you at $5.25, giving you $0.05 of price improvement versus the ask. Your effective trading cost is half the spread: $0.05 per share, or $5 per contract.

Compare this to an illiquid small-cap option where the NBBO might be $1.50 bid / $2.00 ask — a $0.50 spread. Buying at the midpoint ($1.75) still costs you $0.25 per share versus fair value, making the round-trip cost $50 per contract just from the spread.