STD window periods: how long to wait before testing

A test can only find an infection once there is enough of it, or enough of your body's response to it, to measure. The time between infection and that point is the window period. Test too early and you can get a negative result even though an infection is there.

Key points

• Window periods depend on the infection and on the type of test.
• For HIV, CDC gives a range for each test type, from 10 days for the earliest lab test to 90 days for rapid and antibody tests.
• For chlamydia, gonorrhea and trichomoniasis, CDC doesn't publish a single number. Its guidance after a sexual assault is to repeat tests 1 to 2 weeks later.
• The same guidance repeats syphilis tests at 4 to 6 weeks and HIV tests at 6 weeks, with a final check for both at 3 months.
• If you have symptoms, don't wait for a window to pass. See a clinician.

Two kinds of tests

Most STD tests fall into two groups:

• Tests that look for the germ itself. These include nucleic acid tests, often called NAATs or NATs, which detect the germ's genetic material. Chlamydia, gonorrhea and trichomoniasis tests on urine or swabs work this way.
• Tests that look for antibodies. Your immune system makes antibodies over several weeks after an infection. Syphilis, herpes, hepatitis C screening and many HIV tests work this way, so their windows are longer.

Window periods by infection

This table summarizes CDC guidance. The day ranges are what CDC publishes for each test. Where CDC gives no exact window, the table uses the repeat-testing schedule from its sexual assault guidance.

HPV and Mycoplasma genitalium aren't in the table. CDC doesn't recommend routine screening tests for them, so a window period doesn't apply in the same way.

HIV: the test type matters most

CDC says a negative result after the window period means you do not have HIV, as long as you had no new possible exposure in that time. The window depends on the test:

• A lab antigen/antibody test on blood from a vein can usually detect HIV 18 to 45 days after exposure. Check which HIV test a panel uses before you pick a test date.
• A nucleic acid test can usually detect HIV 10 to 33 days after exposure.
• A rapid antigen/antibody test from a finger stick can usually detect HIV 18 to 90 days after exposure.
• An antibody test can usually detect HIV 23 to 90 days after exposure. CDC says most rapid tests and FDA-approved self-tests are antibody tests.

If the exposure happened in the last 72 hours, testing is not the priority. CDC says PEP, a medicine that can prevent HIV, must be started within 72 hours. Go to an urgent care, emergency room or your doctor now.

Chlamydia, gonorrhea and trichomoniasis

These tests detect the germ directly, so they turn positive sooner than blood tests. CDC doesn't publish an exact window. Its guidance after a sexual assault says that if the first tests are negative, STI testing can be repeated 1 to 2 weeks later. The reason it gives is that a repeat test finds infections that "might not have reached sufficient concentrations" to show up the first time.

In practice, a test at 2 weeks or later matches CDC's timing for these three. A test in the first few days can still find an older infection, but it can miss a new one.

Syphilis

CDC's 2024 lab guidance says the first syphilis sore often appears about 3 weeks after exposure, with a range of 10 to 90 days, and that blood tests can be negative early in infection. After a possible exposure, CDC suggests testing at 4 to 6 weeks and again at 3 months.

Hepatitis B and C

CDC says the hepatitis B surface antigen can be detected as early as 1 to 2 weeks and as late as 11 to 12 weeks after exposure. For hepatitis C, CDC's STI treatment guidelines put the average time to a positive antibody test at 4 to 10 weeks, while its testing guidance says antibodies usually take 8 to 11 weeks to become detectable. A test from 11 weeks covers both, and CDC says about 97% of people test positive by 6 months. A hepatitis C RNA test can detect the virus within 1 to 3 weeks, but it is usually ordered as a follow-up, not as a first test.

Herpes

Herpes blood tests look for IgG antibodies, which develop in the first weeks after infection. CDC notes that false negatives are more common early on. When infection is recent, the STI treatment guidelines recommend repeating the test 12 weeks after the possible exposure, and CDC's herpes testing page says it can take up to 16 weeks or more for tests to detect infection. A negative result is most reliable from 16 weeks. If you have a sore, a swab of the sore is the better test, and it doesn't need to wait.

Test now or wait?

• Symptoms now: see a clinician now.
• Possible HIV exposure in the last 72 hours: ask about PEP now.
• No symptoms: this schedule follows CDC's timing. Test at 2 weeks for chlamydia, gonorrhea and trichomoniasis. Test at 6 weeks for HIV and syphilis. Repeat HIV and syphilis at 3 months if the exposure was a real concern.

Our calculator does the date math for you.

Retesting after treatment

A window period is about a new exposure. Retesting after treatment is a separate step:

• Chlamydia and gonorrhea: CDC recommends a new test about 3 months after treatment, whether or not you think your partners were treated.
• Trichomoniasis: CDC recommends retesting women about 3 months after treatment.
• Syphilis: follow-up blood tests at 6 and 12 months.

Don't retest for chlamydia too soon. CDC advises against a NAAT less than 4 weeks after treatment, because leftover dead bacteria can cause a false positive.