National Best Bid and Offer (NBBO)

What Is the NBBO?

The National Best Bid and Offer (NBBO) is the consolidated best available bid price and best available ask price across all registered US securities exchanges at any given moment. It represents the tightest possible spread and the best available prices in the national market system. The NBBO is a regulatory construct established by SEC Regulation NMS to ensure that investors receive the best available prices regardless of which exchange processes their order.

The NBBO is calculated and disseminated by the Securities Information Processor (SIP), which aggregates quote data from all exchanges in real time.

How the NBBO Is Used

Reg NMS Order Protection Rule (Rule 611) prohibits trading at prices inferior to the NBBO. If the NBBO bid is $50.01 and ask is $50.03, an exchange cannot execute a buy order at $50.04 when $50.03 is available elsewhere. Orders must be routed to the venue displaying the best price, ensuring price priority across the national market.

Dark pool pricing frequently references the NBBO. Many dark pool matches occur at the midpoint of the NBBO, providing price improvement to both buyer and seller. If the NBBO is $50.00 bid, $50.02 offer, the midpoint is $50.01, which is better than both the bid and the offer.

Execution quality benchmarks use the NBBO as the reference point. Brokers report what percentage of customer orders received price improvement relative to the NBBO, the average amount of improvement, and the percentage executed at the NBBO versus at an inferior price.

NBBO Limitations

The NBBO only includes round lot quotes (100+ shares), which means better-priced odd lot quotes are excluded. In practice, many sub-100-share orders at better prices exist in the market, meaning the true best available price can be tighter than the displayed NBBO. The SEC has proposed rule changes to address this gap.

The NBBO is also a snapshot that can be stale. In fast-moving markets, the NBBO can change between when your order is submitted and when it reaches the exchange. The SIP consolidation process introduces a small latency that high-frequency traders can potentially exploit, though this speed advantage is measured in microseconds.