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NBBO (National Best Bid and Offer)

The NBBO is the highest displayed bid price and lowest displayed ask price for a given security across all U.S. exchanges and quoting venues at any moment. It represents the best prices at which a retail order can legally be executed under Regulation NMS, which prohibits brokers from trading through a better displayed price on another venue. The NBBO spread — the difference between the two — is the baseline cost of immediacy in U.S. equity markets.

HOW IT WORKS

The NBBO is assembled continuously by the Securities Information Processors (SIPs), which aggregate top-of-book quotes from every national securities exchange — NYSE, Nasdaq, Cboe, IEX, and others — and publish the single best bid and offer in real time.

The calculation is a running comparison across venues:

  • National Best Bid (NBB) — the maximum displayed bid across all venues
  • National Best Offer (NBO) — the minimum displayed ask across all venues
  • NBBO Spread — NBO minus NBB

Only displayed, accessible quotes count. Hidden orders, iceberg reserves, dark pool interest, and quotes from halted or crossed venues are excluded. In active names the NBBO updates thousands of times per second.

Important limitations:

  • The NBBO shows only the top of book. Displayed size at the best price may be 100 shares while real depth sits behind it.
  • The SIP-derived NBBO lags direct exchange feeds by microseconds to milliseconds, creating the structural basis for latency arbitrage.
  • A tight NBBO spread means little for large orders — institutional traders rely on depth-weighted prices, not the touch.

IN TAPEBOARD

Tapeboard displays the real-time NBBO for any symbol in the quote header, alongside displayed size at each side. Use it to:

  • Benchmark executions — compare your fill price to the NBBO bid, offer, and midpoint to evaluate price improvement or slippage.
  • Set limit orders — price limits relative to the current NBBO to join the bid, step ahead of it, or take the offer immediately.
  • Read market stress — a suddenly wide, locked, or crossed NBBO in the Tapeboard feed signals a halt, liquidity withdrawal, or a latency dislocation worth investigating before sending an order.

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