One of the most common questions we get goes like this: "My TV says Apple is at one price, my broker app says something a little different. Which one is wrong?" Usually neither. The two screens are answering different questions, at different moments, from different slices of the market. We spend our days wiring stock prices into TV apps, so here is a plain explanation of every reason two honest prices can disagree, starting with the biggest one.

Delayed vs real-time stock quotes

Most free stock displays, on websites, in apps and on TV, show prices that are delayed, usually by 15 minutes. That is not laziness. The exchanges' own delayed data policies define delayed information as data shown at least 15 minutes after the markets first make it available, and delayed data is treated very differently from real-time data when it comes to fees.

So if it is 10:30 a.m. in New York and the stock is moving, a delayed display is showing you roughly where it was at 10:15. Your broker shows its customers real-time quotes, because you are about to trade on them. On a quiet stock the difference is a few cents. On a busy morning, or a stock that just put out news, it can be a lot more. If you see a gap during market hours, this is the first thing to check, and it explains most of the emails we get.

Why real-time stock data costs money

Exchanges sell their market data. A company that shows real-time prices to the public signs agreements with the exchanges and pays fees, and many of those fees are charged per person who sees the data. Delayed data is much cheaper to distribute, which is why it is the default for anything free.

The fees also depend on who you are. Exchanges split viewers into professional and non-professional subscribers. A non-professional is, roughly, a natural person using the data for their own personal investing who is not working in the securities industry. Professionals pay considerably more for the same prices. Even a regular person can count as professional in some cases, for example when the data comes through a business's account instead of a personal one. That is why your broker made you answer a market data questionnaire when you opened your account: your answers decide which fee applies, and some brokers treat you as professional until you answer.

None of this is secret, but it explains a lot. The real-time price on your broker's screen is not free. Somebody is paying for it, usually the broker, because it wants you trading.

Consolidated quotes vs a single exchange's price

A US stock does not trade in one place. Apple trades on Nasdaq, on the New York Stock Exchange's venues, on Cboe's exchanges, on IEX and on others, plus off-exchange venues. Each one has its own last trade and its own best bid and offer at any moment.

The official consolidated view comes from the securities information processors, often called the SIPs, which collect trades and quotes from every exchange and publish the consolidated tape and the national best bid and offer (the NBBO). When your broker shows you a quote in a screen where you can place an order, SEC rules generally require that quote to be the consolidated one.

Other displays may use something narrower: the last trade from one exchange, or a feed that covers a group of exchanges but not all of them. Those prices are real trades. They just are not the same trades. Two screens can each show a genuine "last price" a few cents apart because one is looking at the whole market and the other at part of it.

Last trade, bid, ask and mid

A price is not one number. There is the last trade, the price at which shares most recently changed hands. There is the bid, the best price someone is currently willing to pay, and the ask, the best price someone is willing to sell at. Some apps show a mid or "mark" price halfway between the two.

A TV display or a market website almost always shows the last trade. A broker's order screen puts the bid and ask front and center, because that is what you would actually get. For a big, heavily traded stock, these are usually within a penny or two. For a thinly traded stock, the last trade might be from several minutes ago and sit well outside today's bid and ask.

Daily change is its own trap. "Up 1.2% today" depends on what you call yesterday's close. Most apps use the official closing price from the regular session. Some compare against the last trade of the evening, after-hours trades included. Same stock, same moment, two different percentages.

Pre-market and after-hours prices

The regular session runs from 9:30 a.m. to 4:00 p.m. Eastern. Nasdaq also lists pre-market trading from 4:00 a.m. to 9:30 a.m. and after-hours trading from 4:00 p.m. to 8:00 p.m. Eastern, and individual brokers set their own extended-hours windows inside that.

Extended-hours trading is thin, so prices can jump around on small orders. Some displays show the extended-hours last trade. Others hold the 4:00 p.m. close until the next morning. If you check your broker at 7:00 p.m. after an earnings report and it shows a stock down 6%, while your TV shows it flat, both can be correct. One is showing the evening session and the other is showing the close.

Why crypto prices never match

Crypto makes all of this worse. It trades 24 hours a day, 7 days a week, on many separate exchanges, and there is no single official consolidated price the way there is for US stocks. Every exchange has its own price, and every app picks a source or blends several.

There is no official close either, so "change today" can mean change since midnight in some time zone, or change over the last 24 hours. If your app and your exchange disagree on Bitcoin by a few dollars and on the daily percentage by a lot, check which definition each one uses before assuming anything is broken.

Refresh intervals and caching

Even two real-time screens using the same feed can disagree, because a price on a screen is a snapshot from the last time it updated. A broker app might stream every tick to your phone. A website might refresh every few seconds, or only when you reload the page. A TV app has to balance freshness against network use and the memory limits of a streaming stick that may be running all day.

Caching adds another layer. Servers and apps keep recent prices for a short time so they are not asking for the same number thousands of times a second. That is normal and healthy, but it means two screens refreshed a few seconds apart can show two different prices for a fast-moving stock. And if a TV has been asleep or the app was in the background, the first thing you see when you come back may be the last price it had, before the next update lands.

How to tell which stock price is right

When two screens disagree, run through this in order:

1. Is one of them delayed? During market hours, this is the answer most of the time.
2. Are you comparing the same field? Last trade on one screen against the bid or ask on the other will never match exactly.
3. Is it outside regular hours? One screen may include pre-market or after-hours trades and the other may not.
4. Is it crypto? Different exchanges, different definitions of "today."
5. When did each screen last update? A few seconds matter on a fast stock.

And one rule that matters more than any of the above: when you are about to place a trade, the only price that counts is the live quote on your broker's order screen. A TV, a website or a news ticker is for watching the market, not for setting a limit price.

If you are curious why so much free market data is delayed, limited or quietly disappearing, we wrote about it in free stock data keeps dying, the sequel to our 2017 post on Yahoo shutting down its finance API.

What MarketCast shows on your TV

MarketCast's main feature is the Stream, a live stock market channel for your TV that plays your stocks, the indexes, the day's movers and headlines with a ticker tape along the bottom. MarketCast Free shows delayed prices and is supported by commercials and sponsors, so expect the kind of gap described above during market hours. Premium is the real-time data package: real-time stock prices, crypto around the clock, no commercials, plus extras like Congress trades and customization. Compare Free and Premium to see everything in each. You can download MarketCast free on Fire TV, Google TV and Apple TV, use it to watch your portfolio on your TV, or turn a spare screen into a stock ticker. Either way, it is for keeping an eye on the market. Your broker is still where the trading happens.