Rapid COVID tests have since become a staple of cough-and-cold aisles across America, and just weeks ago the federal government resumed its periodic distribution of four free tests per household. But the convenience of self-testing comes with a caveat: The onus is on you to report your results.

First, know that test reporting isn’t mandatory in the U.S., so you’re hardly in hot water if you haven’t documented your COVID infection or lack thereof with the Centers for Disease Control and Prevention (CDC) or state or local public health authorities. Though perhaps more people would self-report if it were a requirement, says Dr. Sujata Ambardar, an infectious disease specialist at Inova Fairfax Hospital in Falls Church, Va.

“People probably are not self-reporting because they don’t want to have to not go to work—or they may want to go to work—it’s different reasons, and they may not want other people to know,” Ambardar tells Fortune. “Human nature is that they’ll probably only do it if they have to do it. Once you make it non-mandatory, then they tend not to do it.”

Today, if you get an antigen or PCR COVID test in a clinical setting, it’s still your health care provider’s job to report your results. While you’re well within your rights not to report your home test results, not doing so can come as a detriment to public health.

Between Feb. 1, 2022, and Jan. 1, 2023, an estimated 54 million adult COVID cases were unaccounted for in official records, according to a national study published Sept. 30 in the journal JAMA Network Open. That’s more than twice as many as those documented. At the state level, unaccounted infections ranged from 59,000 in Wyoming to 6.3 million in California. Researchers cited the government-led mass distribution of at-home tests as a possible driver of the discrepancies.

Report COVID results at MakeMyTestCount.org

In theory, Ambardar says, reporting your COVID test results is “just one extra step.” But when that second line appears on the test card, confirming the disease has hit your household, formally documenting the outcome may not be your first priority. Even if you’re negative, you were likely feeling poorly enough to take the test in the first place and may not feel up to self-reporting.

But if and when you choose to do so, visit MakeMyTestCount.org to securely and anonymously report both positive and negative COVID test results. The site is a collaboration between medical data firm Care Evolution and the National Institute of Biomedical Imaging and Bioengineering, part of the National Institutes of Health.

MakeMyTestCount.org is free to use and doesn’t require you to immediately self-report. In fact, your results don’t even have to be recent. As of early October, the site allowed for the input of home test results going back to November 2021. If you need proof of illness for work or school, the site provides documentation. And while over-the-counter tests that screen for both COVID and flu aren’t as common as those that screen for COVID alone, you can report those results on the site, too.

Keep in mind that it’s just as important to report negative results as positive ones. The week ended Sept. 21, national COVID test positivity was 11.6%, CDC records show, down from 13.4% the previous week. If not for the inclusion of negative results, test positivity would always be 100%.

Depending on the brand of COVID test you’re using, you may not have to visit MakeMyTestCount.org at all. Some brands, such as iHealth, offer a free corresponding smartphone app. With the tap of your finger, you can forward your results to the CDC and/or your health care provider. If you have the time, notifying your doctor can help guide the course of COVID treatment in your community, says Dr. Donald Dumford, an infectious disease specialist at Cleveland Clinic Akron General.

“The more we know about the true number of cases of COVID, the better we’re able to understand the transmission of COVID at this point in time, as we go from it being pandemic to endemic, which means it’s just something we live with now,” Dumford tells Fortune. “It also helps us to identify the potential rise of new strains of infection, especially if you’re seeing a strong uptick in cases.”

For more on COVID-19:

• Public health experts are warning of a ‘quad-demic’ this winter. Here’s where flu, COVID, RSV, and norovirus are spreading
• Free, at-home COVID tests are back. Here’s how to order yours
• Got COVID? Here are the new 2024 isolation guidelines
• Could it be COVID? Here are the symptoms to watch out for in 2024
• COVID sickens older adults most severely, but less than half say they’ll get the new vaccine