NBBO: What It Is and How It's Calculated

By Samuel Becker · September 01, 2023 · 5 minute read

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NBBO: What It Is and How It's Calculated

NBBO stands for the National Best Bid and Offer, a regulation put in place by the Securities and Exchange Commission (SEC) that requires brokers who are working on behalf of clients to execute a trade at the best available ask price, and the best available bid price.

The NBBO is a quote available marketwide that represents the tightest spread, e.g. the highest bid price and the lowest ask price for a certain security trading on various exchanges.

Brokers must guarantee at least the NBBO to their clients at the time of a trade, per SEC rules.

How Does “Bid vs Ask” Work in the Stock Market

In order to understand NBBO, investors need to understand the bid-ask price of a security, e.g. a stock. This is also known as the spread (two of many terms investors and traders should know). If an investor is “bidding,” they’re looking to buy. If they’re “asking,” they’re looking to sell. It may be helpful to think of it in terms of an “asking price,” as seen in real estate.

The average investor or trader will typically see the bid or ask price when looking at prices for investment securities. Most of the bid-ask action takes place behind the scenes, and it’s happening fast, landing on an average price. These are the prices represented by stock quotes.

That price is the value at which brokers or traders are required to guarantee to their customers when executing orders. NBBO requires brokers to act in the best interest of their clients.

Recommended: How to Invest in Stocks: A Beginner’s Guide

What Is NBBO?

The National Best Bid and Offer (NBBO) is effectively a consolidated quote of the highest bid and the lowest ask price of a security from all exchanges. NBBO was created by the SEC to help ensure that brokerages offer customers the best publicly available bid and ask prices when trading securities.

NBBO Example

Let’s run through a quick example of how the NBBO might work in the real world.

Let’s suppose that a broker has a few clients that want to buy a stock:

•   Buyer 1 puts in an order to the broker to buy shares of Company X at $10

•   Buyer 2 puts in an order to the broker to buy shares of Company X at $10.50

•   Buyer 3 puts in an order to the broker to buy shares of Company X at $11

Remember, these are “bids” — the price at which each client is willing to purchase a share of Company X.

On the other side of the equation, we have another broker with two clients that want to sell their shares of Company X, but only if the price reaches a certain level:

•   Client 1 wants to sell their shares of Company X if the price hits $12

•   Client 2 wants to sell their shares of Company X if the price hits $14

In this example, the NBBO for Company X is $11/$12. Why? Because these are the best bid vs. ask prices that were available to the brokers at the time. This is, on a very basic level, how calculating the NBBO for a given security works.

💡 Quick Tip: How do you decide if a certain trading platform or app is right for you? Ideally, the investment platform you choose offers the features that you need for your investment goals or strategy, e.g., an easy-to-use interface, data analysis, educational tools.

How NBBO and “Bid vs Ask” Prices Are Calculated

To make those calculations on the fly requires a whole lot of infrastructure. Because the NBBO is updated constantly through the day with offers for stocks from a number of exchanges and market players, things need to move fast.

Most of the heavy lifting in NBBO calculations is done by Securities Information Processors (SIPs). SIPs connect the markets, processing bid and ask prices and trades into a single data feed. They were created by the SEC as a part of the Regulation National Market System (NMS).

There are two SIPS in the U.S.: The Consolidated Tape Association (CTA) , which works with the New York Stock Exchange, and the Unlisted Trading Privileges (UTP) , which works with stocks listed on the Nasdaq exchange.

The SIPS crunch all of the numbers and data to keep prices (NBBO) updated throughout the day. They’re incredibly important for traders, investors, brokers, and anyone else working in or adjacent to the markets.

💡 Quick Tip: When you’re actively investing in stocks, it’s important to ask what types of fees you might have to pay. For example, brokers may charge a flat fee for trading stocks, or require some commission for every trade. Taking the time to manage investment costs can be beneficial over the long term.

Is NBBO Pricing Up to Date?

The NBBO system may not reflect the most up-to-date pricing data. Bid, ask, and transaction data is flying around every millisecond, and it takes time to ingest and process it all. For high-frequency traders that are making fast and furious moves on the market, these small price fluctuations can cost them.

To make up for this lag time, the SEC allows trading via intermarket sweep orders (ISO), letting an investor send orders to multiple exchanges in order to execute a trade, regardless of whether a price is the best nationwide.

The Takeaway

NBBO represents the crunching of the numbers between the bid-ask spread of a security, and it’s the price you’ll see listed on a financial news network or stock quote.

The NBBO adds some legal teeth for investors, effectively forcing brokers to execute trades at the best possible price for their clients.

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Photo credit: iStock/g-stockstudio

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