There are a few possibilities in this scenario, experts tell Fortune. At-home COVID tests “work as well as they always have”—even on new variants like “Pirola” BA.2.86, “Eris” EG.5.1, and “Fornax” FL.1.5.1, Dr. Amesh Adalja, an infectious disease specialist and senior scholar at the Johns Hopkins Center for Health Security, tells Fortune. 

Your test may have given you a false negative, which are far more common than false positives, experts say.

Or you may be performing the test wrong—or at the wrong time.

Are you performing your COVID test wrong?

One reason you might be testing negative when you aren’t: When you performed your nasal swab, you might have sampled a patch of nose that didn’t contain the virus. Or perhaps the patch included the virus, but not enough of it.

“When we sample the nose, we’re grabbing one little patch—a tiny little surface area—when the virus could definitely be replicating somewhere else in the body,” Dr. Stuart Ray, vice chair of medicine for data integrity and analytics at Johns Hopkins’ Department of Medicine, previously told Fortune. 

“The nose is one of the portals through which the virus enters and lives, but it’s also in the mouth and could be harbored deep in the lungs.”

Are you performing your COVID test at the wrong time?

At-home COVID tests not working is a common complaint these days, Raj Rajnarayanan—assistant dean of research and associate professor at the New York Institute of Technology campus in Jonesboro, Ark., and a top COVID variant tracker—tells Fortune.

That’s because you may be testing too early at home. At both the beginning of an infection and at the end, viral loads are not always significant enough to turn a test positive.

Most people with symptoms who test negative initially “test positive after a day or two,” Rajnarayanan says.

What question are you asking your COVID test?

The problem for many people is that they’re asking the wrong question of their at-home COVID test, Adalja says.

Such tests can tell you if you’re able to spread COVID or not—a positive means you are able to, a negative means you’re not able to. But a negative test doesn’t mean you don’t have COVID, Adalja says. It simply means you’re not yet contagious or not contagious anymore, or you may have a different infection causing your symptoms. If you test negative, you may need to test again.

Some additional tips for testing, from the U.S. Centers for Disease Control and Prevention:

• If you have COVID symptoms, test immediately.
• If you test negative using an at-home test, repeat the test again in 48 hours.
• If you were exposed to COVID, test at least 5 full days after exposure.
• If you test negative using an at-home test, repeat the test again in 48 hours.
• If you still test negative, wait 48 more hours and test for a final time.
• In both cases, if you’d rather not wait, you can obtain a PCR, or polymerase chain reaction, test at a doctor’s office. These are more sensitive and tend to be more accurate.