Expiration dates on many at-home tests are outdated. Here’s how to figure out the new one.

Many people have embraced rapid, antigen tests to check whether they are shedding the virus. The hand-held, disposable tests search for viral proteins called antigens and provide results in about 15 minutes.

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U.S. manufacturers had the capacity to make some 320 million at-home antigen tests during the month of July, according to consultancy Health Catalysts Group.

Many people have boxes of rapid tests in their closets and cupboards that they have stockpiled since the Omicron variant pushed case numbers to records last winter. The Biden Administration has delivered more than 350 million free tests, and people can order a third round of free tests from covidtests.gov or buy their own online or at retailers.

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The Food and Drug Administration initially cleared many at-home test kits for a shelf life of four to six months, based on early data from manufacturers.

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But manufacturers continue to collect more data on how long the tests are viable, often using something called a real-time stability test: For a product with a proposed 12-month shelf life, for example, a manufacturer will store it for 13 months, and then test its performance.

As manufacturers have continued testing the longevity of at-home Covid-19 kits, they have sent additional data to the FDA. The agency updates its database of expiration dates based on the data.

That means your tests might last longer than the date on the box, so don’t throw them away. Instead, visit the list of authorized tests on the FDA’s website and look for your brand.

Tests including the BinaxNOW, On/Go, Flowflex, and iHealth now have longer shelf lives than some of their labels indicate. Some tests remain usable for more than a year.

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The expiration dates could be extended again as manufacturers collect more data on the tests’ durability, diagnostics experts said.

The tests could still be usable a few days after the updated expiration date, some diagnostic experts said. The FDA doesn’t recommend using expired tests, since parts of the tests can degrade over time, potentially leading to inaccurate results.

The test itself can also help you determine whether it’s still working, experts said. Make sure the control line is clearly visible and in the right location when taking the tests and that there’s a normal volume of liquid in the dropper, experts said.

If the test is exposed to hot or cold weather, store it at room temperature for at least two hours before using it, the FDA says. Avoid exposing the tests to heat for a long period of time. If the result is unexpected, consider taking a second rapid test after a day or so or a more sensitive PCR test right away.

Cover image: Watchalee Sirikayon Produced by Siemond Chan