When to test after STI exposure: window periods
A “window period” is the gap between exposure and when a test can usually detect infection. Testing too early can miss an active infection. CDC also publishes post-exposure repeat-testing checkpoints, which are not the same thing as detection windows. The right plan depends on the infection, test technology, exposed sites, symptoms, treatment, and clinical context.
Short answer
- Chlamydia & gonorrhea (NAAT): CDC post-exposure guidance says an early negative NAAT can be repeated at 1–2 weeks when no presumptive treatment was given.
- HIV: CDC lists 10–33 days for NAT, 18–45 days for a lab antigen/antibody test, and 23–90 days for antibody tests.
- Syphilis: CDC post-exposure guidance identifies repeat serology at 4–6 weeks and 3 months when an initial result is negative and infection in the source cannot be ruled out.
- Hepatitis: HBsAg can appear about 1–12 weeks after HBV exposure; HCV RNA usually appears at 1–2 weeks and HCV antibodies at 8–11 weeks.
- If a possible HIV exposure was within 72 hours, seek medical advice about HIV PEP now instead of waiting to test.
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Open the STI test window calculatorCDC windows and checkpoints at a glance
| Infection | Test | Window or checkpoint | Meaning |
|---|---|---|---|
| Chlamydia | NAAT at exposed sites | Repeat checkpoint: 1-2 weeks | Repeat-testing checkpoint |
| Gonorrhea | NAAT at exposed sites | Repeat checkpoint: 1-2 weeks | Repeat-testing checkpoint |
| HIV | Lab antigen/antibody test (blood from a vein) | Usually detects at 18-45 days | Detection range |
| HIV | Antibody test, including most self-tests | Usually detects at 23-90 days | Detection range |
| HIV | Nucleic acid test (NAT) | Usually detects at 10-33 days | Detection range |
| Syphilis | Serologic blood testing | Repeat at 4-6 weeks and again at 3 months | Repeat-testing checkpoint |
| Hepatitis B | Hepatitis B surface antigen (HBsAg) | Can appear about 1-12 weeks after exposure | Detection range |
| Hepatitis C | HCV RNA test | RNA usually becomes detectable at 1-2 weeks | Detection range |
| Hepatitis C | HCV antibody test | Antibodies usually become detectable at 8-11 weeks | Detection range |
Compiled from the linked CDC sources. Individual test brands and clinical situations can differ. Check the test instructions and ask a clinician when exact timing matters.
Practical scheduling
- Within 72 hours of a possible HIV exposure: seek medical advice about HIV PEP immediately. It must be started within 72 hours and works best as soon as possible.
- ~1–2 weeks post-exposure: CDC post-exposure guidance allows repeating an earlier negative chlamydia or gonorrhea NAAT when no presumptive treatment was given.
- ~4–6 weeks post-exposure: this overlaps the lab HIV antigen/antibody range and the first CDC syphilis repeat-testing checkpoint.
- ~3 months post-exposure: this reaches the end of the CDC antibody-test range for HIV and a later syphilis follow-up checkpoint in the cited guidance.
- If treated for chlamydia or gonorrhea: CDC recommends rescreening at 3 months because reinfection from untreated partners is common.
If you have symptoms
Don’t wait for a window period. Symptoms (discharge, sores, painful urination, pelvic pain, rash) mean a clinician evaluation today - testing in a symptomatic context is diagnostic, not screening, and the timing/coding rules are different.
Sources: CDC 2025 nPEP recommendations · CDC HIV testing windows · CDC hepatitis C testing · CDC Pink Book: Hepatitis B · CDC HIV PEP · sources checked August 26, 2026.
This page is a decision aid - general information, not medical advice. See methodology for how we rank options and our editorial policy for source and review standards.