Figuring S&P's daily P-E ratio is easy, if you know where to go

— -- Q: Is there a way to find out what the Standard & Poor's 500's price-to-earnings ratio is every day or every week?

A: There seems to be a bit of confusion over the price-to-earnings ratio, judging on a number of questions I'm getting on the topic.

Many readers want to know what the Standard & Poor's 500's historical P-E ratios is. A previous Ask Matt directs readers to an area of S&P's website that provides the index's P-E at the end of each quarter. You can get to S&P's data here. If you click on the link at the bottom of the page that says "S&P 500 Historical Average Price To Earnings Ratio," you'll see a spreadsheet showing the S&P 500's P-E calculated quarterly.

Some readers have been confused by this spreadsheet. Why is the P-E ratio only shown quarterly, instead of daily or weekly? After all, you can calculate the S&P 500's P-E ratio every minute of the day if you want to. The P-E is price divided by earnings. The market price is constantly changing, so the P-E changes, too. Just remember, though, that since earnings are reported by companies each quarter, the denominator will only change quarterly.

If you want to get the P-E ratio every month, or hour, you just need to do a quick division. Divide the S&P 500's value by earnings the past four quarters, to get the trailing P-E.

You can get full instructions on how to perform this calculation here.

Matt Krantz is a financial markets reporter at USA TODAY and author of Investing Online for Dummies. He answers a different reader question every weekday in his Ask Matt column at money.usatoday.com. To submit a question, e-mail Matt at mkrantz@usatoday.com. Click here to see previous Ask Matt columns.