When to Test for COVID-19 After Symptoms and Exposure to Get the Most Accurate Results

COVID-19 testing is an important part of treatment and prevention and there are two different options: PCR and rapid antigen. PCR tests are typically done in a hospital or healthcare clinic setting. But there are some at-home PCR testing options. The rapid antigen test is the most widely available COVID test, providing results right away. But it isn’t as accurate as the PCR test.

No matter which test you use, it can be tricky to know the best time to take a COVID test. And timing can affect how accurate the test result is. Learn more about when your test results are most reliable. 

When should you take a COVID test?

Here’s the latest guidance from the CDC on when to test for COVID infection:

• Test right away if you feel symptoms of COVID infection.

• If you have symptoms and you test negative, test again after 48 hours. 

• If you’ve been exposed to someone with confirmed COVID infection, wait 5 days before testing.

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Even if you haven’t knowingly been exposed, consider testing before you attend a large event or visit someone who’s at high risk. The ideal time to test is 1 to 2 days before the event or visit. 

When to test for COVID after having symptoms

COVID tests are pretty accurate once you have symptoms. This is especially true for PCR tests. 

COVID symptoms can start anywhere from 2 to 14 days after infection with the virus. If you have any symptoms of COVID, test immediately. A positive test is a reliable result — no matter how early you take the test or the type of test. So it’s best to contact a healthcare professional for guidance and treatment options. 

But if you have symptoms and you test negative, don’t assume that the result is definitive. Viral levels in your body might be too low to detect on a test early on in the infection, even if you have some symptoms. A PCR test will give you the most reliable negative result — but most people don’t have easy access to these. And even with home PCR testing kits, results aren’t available right away, since the sample will have to be sent to a lab for processing. 

On the other hand, rapid tests are easy to access and give you immediate results. But a negative antigen result is even less reliable than a PCR test. To be cautious, take another test in 48 hours. If the second antigen test is negative and you still have symptoms, contact a healthcare professional for further guidance. 

When to test for COVID after exposure

If you’ve been in close contact with someone infected with COVID, a COVID test can be helpful even if you don’t have any symptoms. But don’t test right away. Remember, COVID tests aren’t great at picking up tiny amounts of virus in the body.

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Wait at least 5 days after your exposure to test for COVID infection. Using a PCR test will give you the most reliable results, but getting results from PCR tests can take time. If you want faster results, you can use a rapid antigen test. These tests give you results within minutes, but they can be less accurate. 

If you’re using rapid antigen tests, it’s recommended that you test multiple times over the course of several days after your exposure. If you test negative, test again 48 hours later. And if the second test is negative, test for a third time 48 hours later. If at any point you test positive, you have COVID infection.

What type of COVID test should I take?

No matter which you use — PCR or rapid antigen test — COVID tests are more accurate when they’re positive and less accurate when they’re negative. That means a negative result could be a false negative. However, a negative test result is more reliable if you retest as negative. 

Let’s look at the differences between the two tests and how accurate they are at detecting COVID infection.

Molecular tests (PCR tests)

Molecular tests look for viral genetic material. These are considered the best available tests for detecting active infection. 

But they’re not perfect. For one, they don’t give immediate results. You also shouldn’t use a PCR test if you’ve tested positive for COVID-19 in the past 90 days. Molecular tests pick up very small amounts of viral DNA, so it could remain positive for some time if you’ve had a recent infection. 

Otherwise, the risk of a false-positive result is very low. In other words, if your test is positive, you have COVID infection 

But, since virus levels are very low on the first day of infection, these tests may not detect the virus. This is called a false negative result. In fact, some data estimates that 100% of molecular tests will be falsely negative on the first day of infection. 

As the infection advances and the virus makes copies of itself, there’s more viral DNA for the COVID test to detect. So, by day 5 of infection, the chance of a false negative result goes down to 40%. By day 8, that number goes down to 20%. The test becomes better at avoiding false negatives as the infection advances. 

Antigen (rapid) tests

Antigen tests test for specific surface proteins on the virus that causes COVID. You should use a rapid test if you have symptoms of COVID. 

Rapid COVID antigen tests are convenient, quick, and affordable. You can pick up these test kits without a prescription at your local pharmacy. They deliver results in about 15 minutes. These tests have become the dominant COVID tests because of their convenience. They’re not perfect, but they’re easy to use. Plus, they provide immediate results wherever you are. 

Most rapid antigen tests have very high specificity (very few false positive results). In other words, like with PCR tests, if you get a positive result on a rapid test, then you have COVID infection. 

On the other hand, antigen tests are less sensitive than PCR tests. That means they have a higher risk of false negative results. This is because COVID antigen tests aren’t as good at detecting low levels of the virus. So, a single negative result on a rapid test isn’t very reliable — especially during the first few days of an infection. 

Is the optimal testing window the same for PCR, antigen, and COVID antibody tests?

The ideal timing for testing is similar for all viral tests (PCR or rapid tests):

• If you have symptoms, test immediately.

• If you’ve been exposed to the virus that causes COVID but don’t have symptoms, wait 5 days to test.

COVID antibody tests, on the other hand, are an entirely different type of test. A viral COVID test (PCR or rapid test) can tell you if you have an active COVID infection, but a COVID antibody test doesn’t. 

Instead, a COVID antibody test looks for whether you have antibodies to the virus that causes COVID in your blood. Antibodies are part of your body’s immune response to a past COVID infection or COVID vaccination. It typically takes 1 to 3 weeks after an infection or vaccination for an antibody test to show positive. 

COVID antibody tests were common early on in the pandemic, but they’ve fallen out of favor more recently. This is because so many people have either been infected by COVID or vaccinated against it at this point. These tests are no longer as useful as they were when COVID infection was brand new.

When should you retest after a positive COVID result?

If you’re trying to find out whether you have COVID or not, you don’t need to retest after a positive COVID result. Positive results on COVID tests (whether PCR or rapid) are very reliable. There’s no need to confirm this with another test.

Experts used to recommend retesting for COVID to find out when you were no longer contagious and could stop isolating. These recommendations have changed though. The CDC currently recommends that you can return to normal activities after COVID once you can say “yes” to both of these statements: 

• Your symptoms have resolved.

• You’ve been fever free for 24 hours. 

The CDC no longer recommends retesting for COVID before returning to normal activities.

Does recent infection or vaccination affect the timing window for testing?

Generally, no. Get tested if you think you might have a new COVID infection. A positive COVID test means you have COVID infection — even if you were vaccinated recently. But it depends on the kind of test you’re using — and if you have symptoms (more on this below).

How does vaccination affect testing? 

A COVID vaccine can’t make you test positive for COVID infection. COVID vaccines don’t contain the virus that causes COVID, so they can’t cause an active infection.

Vaccination also doesn’t affect the timing window of testing. If you have symptoms, test immediately. If you don’t have symptoms but were exposed to the virus that causes COVID, wait 5 days before testing. 

You can still get (and pass on) the virus that causes COVID if you’re vaccinated. 

How does a previous COVID infection affect testing?

The same is true if you’ve had COVID before. If you have symptoms, then it doesn’t matter whether you were previously infected. You should test right away. 

But let’s look at this scenario:

• You don’t have symptoms. 

• But you were exposed to the virus. 

• And you’ve had a COVID infection in the last 90 days.

In this case, interpreting test results can be a little tricky. It’s recommended to use a rapid antigen test. That’s because a PCR test might pick up dead virus particles from your previous infection. 

If you have questions about testing, contact a healthcare professional for more guidance.

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Written by:

Angela Dunn, MD, MPH

Angela Dunn, MD, MPH, is a public health physician practicing in Utah, with a focus on serving under-resourced communities.

Edited by:

Karla Robinson, MD

Karla Robinson, MD, is a medical editor for GoodRx. She is a licensed, board-certified family physician with almost 20 years of experience in health through varied clinical, administrative, and educational roles.

Reviewed by:

Farzon A. Nahvi, MD

Dr. Nahvi is an emergency medicine physician and author of “Code Gray: Death, Life, and Uncertainty in the ER.” He works clinically at Concord Hospital in Concord, New Hampshire, and is a clinical assistant professor of emergency medicine at the Geisel School of Medicine at Dartmouth. Prior to this, he worked as an ER physician and clinical assistant professor of emergency medicine at the Mount Sinai Health System, NYU Langone Health, NYC Health + Hospitals/Bellevue, and the Manhattan VA. He is a graduate of Cornell University and NYU School of Medicine.

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