What "Real-Time" Market Data Actually Means

Market data is a product, and exchanges sell it. That single fact explains almost everything about why quotes on free websites behave the way they do.

The consolidated tape

US equity trades and quotes are aggregated into consolidated feeds — the SIP. Redistributing that data in real time requires a licence and per-user fees. Delaying it by 15 minutes does not. That is the entire reason the 15-minute delay is an industry convention rather than a technical limitation.

What this means for you

• Free quotes are usually delayed. If a site does not say, assume they are.
• Your broker generally shows you real-time data for the accounts you trade in, because they license it.
• Delayed data is perfectly adequate for research and for long-term investing. It is not adequate for trading decisions measured in minutes.

How we handle it

NYStocks labels its data source on every page that shows prices, including the timestamp of the last update. When no market data provider is configured, the site says so explicitly and shows clearly-marked sample figures rather than passing generated numbers off as quotes. If you are ever unsure what you are looking at, the banner at the top of the data will tell you.