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200-day moving average sends buy, sell signals for your stocks
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S&P 500 index (blue) and its 200-day moving average (silver), four years.


Q: Investors often refer to moving averages, such as the 200-day moving average. Why does the moving average change so much and why is it different according to different websites?

A: The 200-day moving average is just the latest of the many stock market indicators to get mainstream attention.

A few years ago, as market volatility increased, the volatility index or VIX, a "fear gauge" that measures how nervous investors are, caught on. The VIX went from an indicator followed mostly by traders to one watched by many investors. You can read more here about the VIX.

The 200-day moving average is based on a stock's price history. Such indicators are called "technical indicators" because they're based on trading activity rather than on a company's fundamentals, such as revenue and earnings.

The 200-day moving average is being more closely watched, perhaps, because it has been a useful guide in the past. It works like this: When stocks rise above their 200-day moving average, the thinking goes, that's a good sign and means you should be buying. When stock prices sink below their 200-day average, that's a giant "Look out below!" warning, and you should sell.

The 200-day moving average was especially helpful during the market's recent volatility, as you can read here.

Now that you understand why you should care about the 200-day average, you might want to know how it's calculated. It's a fairly simple calculation. You take an investment's closing values each day for 200 trading days, add them up and divide by 200. This is called the simple moving average, or SMA.

To answer your question, the value of the 200-day moving average is always based on the most recent 200 days, so it will change daily — that's the "moving" part. The investment's latest closing price will be added to the calculation while the oldest closing price is removed.

There are more elaborate ways to calculate the 200-day moving average. Some calculate it by using the median price or factoring in high and low prices during the day. Some websites, including, also provide the so-called exponential moving average, or EMA. With the EMA, recent prices are given more weight in the average calculation. But really, the beauty of the 200-day moving average is its simplicity, and I don't see any reason to tamper with that.

The fact you're seeing different values for the 200-day moving average from different websites probably stems from either differences in the calculation or timing. You'll want to pay close attention to the way the site calculates the average.

I can't speak for other sites. But I can urge you to get the 200-day simple moving average from Just enter the name or ticker symbol of any stock or market index in a Get a Quote box at and click the Go button. Next, click the Charts tab. Choose SMA in the Moving Average drop-down box on the right-hand side of the page and then enter 200 in the box next to it. Click the Draw Chart button. You'll see a graphical representation of the 200-day moving average for your stock or index. If you're interested, you can get the EMA, too.


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