Prices are going up for some of the cheapest and most popular at-home Covid-19 test kits in the U.S.

Walmart Inc. and Kroger Co. are raising their prices for BinaxNOW at-home rapid tests, after the expiration of a deal with the White House to sell the test kits at cost for $14.

The two U.S. retail giants and Amazon.com Inc. agreed with the...

Prices are going up for some of the cheapest and most popular at-home Covid-19 test kits in the U.S.

Walmart Inc. and Kroger Co. are raising their prices for BinaxNOW at-home rapid tests, after the expiration of a deal with the White House to sell the test kits at cost for $14.

The two U.S. retail giants and Amazon.com Inc. agreed with the Biden administration last summer to discount the tests, which are made by Abbott Laboratories and generally cost $24 or more for a box with two tests.

Abbott Laboratories’ FDA-approved BinaxNOW kit is among the most commonly used rapid Covid-19 antigen tests in the U.S.

Photo: Paul Hennessy/Zuma Press

BinaxNOW, approved by the U.S. Food and Drug Administration, is among the most commonly used over-the-counter, rapid antigen tests, which have been in high demand as the highly contagious Omicron variant spreads across the U.S.

The deal with the White House expired in December, and Walmart said this week that it is raising the kits’ price to $19.98 a box. Kroger now sells them for $23.99. The BinaxNOW tests aren’t currently available on Amazon.

Pharmacy chains CVS Health Corp. and Walgreens Boots-Alliance Inc., along with other big retailers, have been selling the tests for $23.99 a box. Other retailers already are charging even more.

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Even at the higher prices, tests are difficult to find. BinaxNOW is sold out on many major retailers’ websites or takes more than a week to arrive. A Walmart spokeswoman said the BinaxNOW tests are more readily available in physical stores.

Covid-19 tests—both at-home kits and those done on location in clinics or at drugstores—remain costly and difficult to find in many places as the Omicron-driven surge pushes many Americans to seek out the diagnostic tools. The Biden administration has said it is working to expand access to free testing and has pledged to distribute 500 million free at-home tests. Some cities and states have established similar programs.

The White House said last month that it would begin delivering at-home tests in January and that they would be available to the public free by mail through a new website. Officials haven’t provided details of the plans to mail out tests or to cover the costs of testing.

Kroger now sells BinaxNOW Covid-19 test kits for $23.99 a box.

Photo: USA TODAY NETWOR/Reuters

“When the prices are that high, people will rationalize not using a kit. They’ll wait until they’re sick or need it for school or something,” said Eric Feigl-Ding, an epidemiologist and health economist and a senior fellow at the Washington, D.C.-based Federation of American Scientists. “The problem with this pricing, besides creating a lack of access, is that it creates a perverse incentive for people not to use them.”

The tests need to be free or cost closer to $1, as is the case in much of Europe, to be an effective tool, Dr. Feigl-Ding said. That is because people who have few or no symptoms can still spread the virus.

The cheapest tests available on Amazon cost $17.98 and $24.88, and the e-commerce site says they would likely arrive in mid- to late January. In places where demand for testing is especially high, many people face hourslong lines or scarce appointment slots. Lab-processing times have also lengthened.

Amazon and the White House didn’t immediately respond to requests for comment. Spokespeople for Walmart and Kroger said they fulfilled their commitment to sell tests at-cost for three months and are taking steps to make tests more available.

Write to Sharon Terlep at sharon.terlep@wsj.com