National Best Bid and Offer (NBBO)
The National Best Bid and Offer (NBBO) is the highest available buy price and the lowest available sell price for a security across all registered US exchanges and market centers at any given moment.
The NBBO is the foundational price reference for US equity markets. At any point during the trading day, dozens of venues — NYSE, NASDAQ, CBOE, IEX, and numerous other exchanges and alternative trading systems — may each display bids and offers for the same stock at different price levels. The NBBO consolidates all of those quotes into a single best bid and best offer, giving market participants a unified view of the tightest spread available nationally.
Brokers are legally required under SEC Regulation NMS to execute client orders at prices equal to or better than the NBBO. This is the trade-through rule in practice: an order routed to a venue quoting an inferior price when a better price exists elsewhere is a regulatory violation. The NBBO therefore acts as both an informational benchmark and a compliance floor.
The NBBO is calculated and disseminated continuously by Securities Information Processors (SIPs) — specifically the Consolidated Tape Association (CTA) for NYSE-listed securities and the UTP Plan for NASDAQ-listed securities. These plans collect quote data from every participant exchange and publish the consolidated best bid and offer in real time.
For retail investors, the NBBO directly determines the price they receive when buying or selling shares through a broker. Payment for order flow arrangements, where brokers route retail orders to wholesale market makers, are evaluated in part against whether the resulting execution equals or improves upon the NBBO. Price improvement — executing at a price better than the NBBO — is a metric many brokers highlight in their execution quality disclosures.
The NBBO can change hundreds of times per second in actively traded stocks, reflecting the speed at which electronic market makers update their quotes. In fast-moving markets, a stale NBBO quote can be filled at a different price, leading to what is known as a fill outside the quoted spread, which brokers must explain under best execution obligations.