Why do Stock-Market prices that websites quote have a delay?

it is most likely because they offer the information pretty much, free to you. if you pay for that information you can get streaming price data. understand what I mean?
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The Stock Exchange charges large fees for live prices and the professional traders are willing and able to pay. If a website shows you them for free it is because they have to have the time delay built in.
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Yes. They need to fix that. Streaming quotes are delayed on most websites.

You should develop a website that gives up to the second " streaming quotes" to everyone.

Then I'd visit your site to check on my stocks. Hehe
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If you really need real time information then you can visit MSN Money.
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The reason is because to have real time quotes you have to subscribe to a service and those services are very costly. Services such as Bloomberg, Reuters, etc…Yahoo and Google arent going to pay for that service because there are licensing agreements for users, which logistically they can't account for the users. And yes its a huge atvantage to people with real time quotes, imagine how much a stock can move in 15-20 min.
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