Quick definition The NBBO is the best bid and best ask available across all US trading venues at any moment, determined by the SIP feed. Brokers must route orders to achieve the NBBO. What it is The NBBO is calculated by the Securities Information Processor (SIP) from data submitted by all US trading venues. If NASDAQ has bid 150.40 and NYSE has bid 150.39, the NBBO bid is 150.40 (the higher one). The NBBO is the official measure of best available price. It is used to determine compliance with the best execution rule. Why it matters Brokers are required to route orders to achieve the NBBO or better. If a broker routes a customer order to a venue where the price is worse than the NBBO, the broker is in violation of Regulation NMS (National Market System). The NBBO also affects trading algorithms and risk management. Traders monitor the NBBO to understand market conditions. NBBO versus BBO The NBBO is the best bid-offer across all US venues. The BBO is the best bid-offer on a specific venue. In fragmented markets, the NBBO may differ from the BBO on any particular venue. Practical example You want to buy shares. The NBBO shows bid 150.40, ask 150.41. Your broker must route your order to a venue that offers ask 150.41 or better. If the broker routes you to a different venue with ask 150.50, they have violated best execution rules. Regulatory enforcement The SEC monitors NBBO violations. Brokers that consistently fail to achieve the NBBO face regulatory action and fines. Best execution is a core requirement of modern market regulation. SIP delays The SIP publishes the NBBO with a delay of 100-250 milliseconds. This delay is why some traders prefer direct exchange feeds (which are faster) for real-time decisions. However, for compliance purposes, the SIP NBBO is the official one. See also - Best Bid-Offer (BBO) - Securities Information Processor (SIP) - Best Execution - Regulation NMS
