Educational only, not financial advice. Market rules and thresholds can change — verify current specifics with the exchanges or your broker.

The NBBO (National Best Bid and Offer) is the highest bid and lowest offer available across all exchanges at any moment — the benchmark your broker must consider when filling your order. It’s the yardstick of a fair fill.

What it is

Stocks and options trade on many venues, each with its own bid and ask. The NBBO consolidates them into the single best bid (highest price a buyer will pay anywhere) and best offer (lowest a seller will accept anywhere). Under regulation, your order should generally be filled at the NBBO or better — so it’s the reference point for whether you got a fair price.

Why it matters

The NBBO is why you can trust that a marketable order fills at a competitive price even though the market is fragmented across venues. It’s also the baseline for price improvement (filling better than the NBBO). The tighter the NBBO spread, the cheaper it is to trade — another reason liquid strikes matter.

The NBBO is the whole market’s best price in one number — the standard your fill is measured against, no matter which venue actually executes it.

What it means for a scalper

You benefit from the NBBO on every trade — it’s why fragmented markets still give retail competitive prices. On liquid SPY options the NBBO spread is tiny (a penny or two). Understanding it demystifies fills and connects to payment for order flow and price improvement.