When you see a stock’s price go up or down, a market’s trading volume and percentage change fluctuate, or the constantly changing numbers of a market index march across your screen—that’s real-time data. Just above the quote summary box on the quote summary page is free real-time data provided by BATS Exchange, which matches up buy and sell stock orders.

This data is available during market hours and before the markets open. Note, however, that BATS Exchange data does not necessarily represent the best bid or ask prices in the marketplace.

Because you will experience some delays with free real-time data, you might want to consider subscribing to our premium service, Yahoo! Real-Time Quotes (which includes MarketTracker). For a modest monthly fee, you’ll get up-to-the-second quotes, bid/ask prices, and relevant news headlines immediately on all Yahoo! Finance pages and My Yahoo!.