LOS ANGELES—If your website traffic plummets suddenly Tuesday, you can blame it on “Mobilegeddon.”

Google, which dominates online search, is launching a new algorithm Tuesday to favor sites that are “mobile friendly.” This means users that use Google to search on their smartphone may not find many of their favorite sites at the top of the rankings. Sites that haven’t updated could find themselves ranked way lower, which in turn could mean a huge loss of business.

Search giant Google, which has a 65% market share of U.S. Internet searches, wants sites to load quickly and be easy to navigate on a mobile phone.

Google is doing this because it wants consumers to “find content that’s not only relevant and timely, but also easy to read and interact with on smaller mobile screens,” Google said in a statement.

The new update will not affect results from desktop searches.

Google’s last big algorithm update, code-named Panda, impacted “11% of all search results,” says Danny Sullivan, the editor of the SearchEngineLand website. “It was a big shakeup, and this one could be even more dramatic.”

A website ranked No. 1 or No. 2 in a search query could hypothetically fall to ninth or tenth place, causing a loss of thousands of dollars in potential business, says independent analyst Greg Sterling.

In 2012, Demand Media posted a $6.4 million loss in an earnings report, and blamed the loss on changes to Google’s Panda update, which removed the firm from top spots.

Just over half of all searches done on Google are now performed through mobile devices, says Sullivan, a number that continues to grow, as more folks transition to spending more and more time on smartphones.

(Sullivan’s website came up with the term “Mobilegeddon,” in March, a play on a recent Los Angeles mini-crisis called “Carmeggedon,” when freeways were closed for several weekends.)

Worried about your website? Google has a “Mobile-Friendly” test page in its developer section. Just type in the URL and see if it passes. The URL: https://www.google.com/webmasters/tools/mobile-friendly/.

USA TODAY tested many top brands into the tool Monday, and came up with many that passed the test–and many that didn’t. Companies that need to update their sites quickly included restaurant chains California Pizza Kitchen and Coco’s, fashion icon Versace, candy manufacturer Sees andand European airline Ryanair, according to Google.

Website TechCrunch found that 44% of the Fortune 500 companies failed the mobile friendly test.

Overall, “As many as 40% of top websites are not currently mobile friendly,” says Sterling. “There’s a big category of people who have completely ignored mobile.”

So what to do if your website doesn’t pass the Google Mobile Friendly test?

Some tips:

–Call your local website host. Many have tools in place to transition your website. GoDaddy, the top provider of website addresses and hosting, offers a tool to completely rebuild your website to make it mobile friendly, and charges $1 monthly for the service. Competitor Bluehost has a tool that’s less time consuming and potentially cheaper. For a one-time fee of $25, it’s goMobi tool builds a smaller, mobile version of your site.

–Go to a service like dudamobile for a more robust, yet smaller version of your website, starting at $5 monthly.

–Get in touch with a local webmaster (try Craigslist and other local forums) to farm out the work, which would probably make the mobile site look more like the original, main site for the computer.

Finally, if you’re a small business and can’t get this done by Tuesday, no need to panic, says Sterling.

Most local businesses are found these days, not via their website, but through directory services like Yelp and Google’s local search listings.

“You typically go to Google and look up car repair, for instance,” he says. “The local listings show up first, not usually the website.”

So his advice to the small business owner is to make sure all your local information is current and up to date in Yelp and on Google’s MyBusiness section.

“They still need to update their website, but this buys them time,” he adds.

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