National Best Bid and OfferNBBO
The NBBO is the highest bid and lowest offer for a US stock across all exchanges at a moment in time. Under US rules, brokers generally must not execute customer orders at prices worse than the NBBO.
The NBBO is the highest bid and the lowest offer for a US stock across all trading venues at any moment. It is the reference price for US execution rules. Other countries use different rules and benchmarks.
- Category
- Market Structure
- Reading time
- 3 min
- Also called
- National best bid and best offer
- Updated
The NBBO in plain words
The NBBO is a stock's best bid and best offer across all US venues, worked out continuously by a consolidator or by the firm itself.1
The Order Protection Rule requires trading centres to have procedures that stop trades happening at worse prices than protected quotes shown elsewhere, apart from specific exceptions.2
A quote is only protected if it can be hit instantly and automatically.2
How the NBBO works
Venues quote
Each exchange shows its own best bid and offer.
Consolidate
The best prices are gathered from all venues and updated continuously.1
Protect quotes
Only quotes that can be filled immediately and automatically are protected.2
Prevent trade-throughs
Trading centres must stop trades from happening at worse prices than protected quotes elsewhere, with limited exceptions.2
Use penny increments
For stocks priced at $1 or more, orders and quotes can't be in increments smaller than one cent (the sub-penny rule).2
Check your fill
Compare your price with the NBBO at order time.
Worked examples
Example 1 — Building the NBBO
30.01 / 30.03Hypothetical: A 30.00/30.04, B 30.01/30.05, C 29.99/30.03.
| Best bid | 30.01 (B) |
| Best offer | 30.03 (C) |
Combining the best bid and best offer from every venue gives the NBBO.1
Example 2 — Trade-through
−0.02A hypothetical buy fills at 30.05 while 30.03 is protected.
| Overpaid | 0.02 per share |
The rules are designed to block trades at worse prices than protected quotes elsewhere, so this should rarely happen.2
Example 3 — Thin top
Book walksHypothetical NBBO shows only 100 shares at the offer.
| Order | 5,000 |
The NBBO only reflects the size displayed, and thin displayed depth points to a problem rather than a healthy market.3
NBBO vs single-venue quote
| Aspect | NBBO | Single venue BBO |
|---|---|---|
| Scope | All protected US venues | One exchange |
| Use | Execution benchmark | Local book |
| Spread | Tightest | Often wider |
| Rule basis | Regulation NMS | Venue rules |
Where the NBBO matters
Fill quality
Judging Slippage.
Spreads
The true Bid-Ask Spread.
Order types
Market Order vs Limit Order pricing.
Brokers
How a Broker routes.
Advantages and disadvantages
Advantages
- Single reference price for US stocks.
- Protects displayed quotes.
- Supports best execution checks.
Disadvantages
- Covers only displayed size.
- Can be stale by milliseconds.
- US-only concept.
- Ignores fees and hidden liquidity.
Going deeper
Read as far as you need. Each level builds on the one before it.
Common mistakes
Assuming size is unlimited
Only shown size is at the NBBO.
Ignoring timing
Quotes change in milliseconds.
Applying it outside the US
Other markets use other rules.
Forgetting fees
Net price matters.
Check your understanding
Test yourself before moving on. Each answer comes with an explanation.
Key points to remember
- NBBO = best bid and best offer across US venues.
- It is a benchmark for execution.
- Protected quotes must be automatically accessible.
- It shows only displayed size.
- It is a US concept; rules differ elsewhere.
Frequently asked questions
Is the NBBO used in Europe?
Can I trade better than the NBBO?
Who publishes it?
Further learning
- Bid-Ask Spread
Spread basics.
- Exchange
Venues in the NBBO.
- Slippage
Fill quality.
- Order Book
Depth beyond the top.
Sources
This article is written in our own words. The sources below support the specific facts, rules and figures marked with a number in the text. Links open the original publisher’s page.
- U.S. SEC (eCFR). 17 CFR 242.600 — NMS security designation and definitions (opens in a new tab) Checked .
- U.S. SEC. Regulation NMS (Final Rule summary) (opens in a new tab) Checked .
- U.S. SEC. Regulation NMS Adopting Release 34-51808 (opens in a new tab) Checked .
Educational content, not financial advice. Examples use hypothetical prices and simplified costs; actual fees, margin rules and regulations vary by broker, market and country. We are not affiliated with any publisher linked above. Last reviewed . Report an error or request a source credit.