A window period is the time between catching an infection and when a test can reliably detect it. If you test during the window, you might get a negative result even though you have the infection. That's why timing your test matters as much as getting one.
STI window period chart
Times are counted from the date of the possible exposure. They're the points by which tests reliably pick up an infection, though many infections show up sooner. Where sources disagree, we show the range and say so.
| Infection | Test type | Window period | Notes and source |
|---|---|---|---|
| Chlamydia | NAAT (urine or swab) | 2 weeks | BASHH: if you're tested within 2 weeks of a possible exposure, come back for a repeat test 2 weeks after that exposure [1]. The CDC doesn't publish a specific figure. |
| Gonorrhea | NAAT (urine or swab) | 2 weeks | BASHH: infection can't be ruled out if you test within 2 weeks of contact [2]. |
| Syphilis | Blood test | Up to 12 weeks (3 months) | BASHH: some syphilis blood tests (RPR) usually turn positive around 6 weeks after infection, but a negative within 3 months can't rule out early syphilis, so repeat at 3 months after a high-risk contact [3]. |
| HIV | NAT (viral RNA, lab blood test) | 10–33 days | CDC [4]. UK guidelines don't recommend RNA tests for routine diagnosis [5]. |
| HIV | Antigen/antibody lab test (4th generation, blood from a vein) | 18–45 days | CDC gives 18–45 days [4]. UK guidelines use 45 days [5]. |
| HIV | Rapid antigen/antibody (finger-prick) | 18–90 days | CDC [4]. |
| HIV | Antibody test (most rapid tests and self-tests) | 23–90 days | CDC gives 23–90 days [4]. UK guidelines use 90 days for all point-of-care tests [5]. |
| Hepatitis B | Blood test (HBsAg) | 1–12 weeks | CDC: detectable as early as 1–2 weeks and as late as 11–12 weeks after exposure [6]. |
| Hepatitis C | RNA blood test | 1–2 weeks | CDC [7]. |
| Hepatitis C | Antibody blood test | Usually 8–11 weeks | CDC [7]. After a negative result, the NHS may advise testing again in 6 months [8]. |
| Trichomoniasis | NAAT (swab or urine) | Not formally defined | The CDC and BASHH treatment guidelines don't give a window period [9]. The NHS says symptoms can start 5–28 days after infection [10]. |
| Herpes (HSV) | Swab of a sore (PCR); blood antibody test | Antibody test: repeat at 12 weeks if recent infection suspected | A swab of a sore is the most sensitive test. Antibodies develop in the first weeks, and the CDC advises repeating an antibody test 12 weeks after a suspected recent infection. Routine herpes blood testing without symptoms isn't recommended [11] [12]. |
NAAT = nucleic acid amplification test. NAT = nucleic acid test. HBsAg = hepatitis B surface antigen. Ranges reflect variation between people. A test at the start of a range catches some infections, and a test at the end catches most.
Where the sources differ
- HIV lab tests: the CDC gives a range of 18–45 days for 4th-generation lab tests. UK guidelines simply use 45 days, because they base advice on the point by which almost everyone (99%) would test positive [5]. Both put the upper end at 45 days.
- HIV rapid and self-tests: the CDC gives a range of 18–90 or 23–90 days depending on the test. UK guidelines use 90 days for all point-of-care tests [4] [5].
- The NHS "7 weeks" rule of thumb: the NHS says STIs can take up to 7 weeks to show up on a test and suggests waiting that long for a screen if you have no symptoms [13]. That's a sensible general rule, but syphilis (up to 12 weeks) and rapid HIV tests (up to 90 days) can take longer, so a clinic may ask you to come back.
- Trichomoniasis: no major guideline we checked gives a formal window period. Ask the clinic when to test.
What to do after a possible exposure
- HIV risk in the last 72 hours? Go now to a sexual health clinic or A&E/ER and ask about PEP. It must be started within 72 hours [14].
- Got symptoms? Get checked straight away. Don't wait for the window period to pass.
- No symptoms? You can test now for a baseline, then retest once the relevant window periods have passed. Clinics often do both.
- Note the date. Window periods count from the exposure, so write down when it happened.
- Use protection or hold off with new partners until you have your results.
Wondering how often to test when nothing in particular has happened? See how often you should get tested for STIs.
BodCount lets you log STI tests and results on your iPhone, keep a history of when you last tested, and see which partners fall within the window if a result comes back positive. Learn about the STI test tracker.
Track your tests in BodCountSources
- BASHH. UK national guideline for the management of infection with Chlamydia trachomatis, 2026. Section: window period.
- BASHH. National Guideline for the Management of Infection with Neisseria gonorrhoeae, 2025. Section 9.1.10: timing of testing.
- BASHH. UK guidelines for the management of syphilis, 2024. International Journal of STD & AIDS.
- CDC. Getting Tested for HIV (window periods by test type).
- BHIVA/BASHH/BIA. Adult HIV testing guidelines, 2020.
- CDC. Epidemiology and Prevention of Vaccine-Preventable Diseases (Pink Book), Chapter 10: Hepatitis B.
- CDC. Clinical Screening and Diagnosis for Hepatitis C.
- NHS. Hepatitis C.
- CDC. Trichomoniasis, STI Treatment Guidelines, 2021.
- NHS. Trichomoniasis.
- CDC. Genital Herpes, STI Treatment Guidelines, 2021.
- BASHH. Summary Guidance on Testing for Sexually Transmitted Infections, 2023.
- NHS. Sexually transmitted infections (STIs).
- CDC. Post-Exposure Prophylaxis (PEP).
Frequently asked questions
What is an STI window period?
It's the time between being exposed to an infection and when a test can reliably detect it. A negative result during the window period might be a false negative, so you may need to retest later.
How long after sex should I wait to get tested?
It depends on the infection. Chlamydia and gonorrhea tests are reliable from about 2 weeks. HIV lab tests are reliable at 45 days, and rapid tests at up to 90 days. Syphilis can take up to 12 weeks. The NHS suggests waiting about 7 weeks for a general screen if you have no symptoms, though a clinic may ask you back for some tests.
Is a negative HIV test at 4 weeks accurate?
Many infections are picked up by then, but not all. The CDC says a 4th-generation lab test can detect HIV 18–45 days after exposure, and UK guidelines treat 45 days as reliable. If you test earlier and get a negative result, test again after the window period.
What is the window period for chlamydia and gonorrhea?
About 2 weeks. UK BASHH guidance says that if you test within 2 weeks of a possible exposure, you should come back for a repeat test 2 weeks after the exposure.
Can I test for herpes if I don't have symptoms?
Routine herpes blood tests aren't recommended for people without symptoms by either the CDC or BASHH. If you have a sore, a swab of the sore is the best test. If a recent infection is suspected, the CDC advises repeating an antibody test 12 weeks later.
Is this medical advice?
No. This is general information, not medical advice. Talk to a clinician or sexual health clinic about your own situation.