Wait until the test can actually detect the infection. For chlamydia and gonorrhea, a urine or swab test is generally reliable about two weeks after exposure. HIV depends on the test used — roughly 10 to 90 days. Syphilis and hepatitis use blood draws with their own windows. Testing too early can give you a falsely reassuring negative.
| Item | Days after exposure |
|---|---|
| Chlamydia / gonorrhea (NAAT) | ~14 |
| HIV — NAT | 10–33 |
| HIV — antigen/antibody | 18–45 |
| HIV — rapid antibody | 23–90 |
How an STD test actually works
The sample is simpler than most people expect. For chlamydia, gonorrhea, and trichomoniasis, a clinic collects a urine cup or you self-collect a swab — vaginal, rectal, or throat depending on the exposure — and the lab runs a NAAT, a test that copies and detects the organism's genetic material CDC chlamydia guidelines. For HIV, syphilis, and hepatitis, a small blood draw goes to the lab. You're in the chair for minutes, and results come back in a day or a few.
How you feel tells you nothing reliable. Many STIs cause no symptoms at all, so a person can carry and pass an infection while feeling completely fine. Only a test tells you your status, and screening is what catches silent infections before they cause harm. If you want the full step-by-step on samples and providers, you can get tested and read our complete walkthrough there.
When to test after exposure: the window period
Every test has a window period — the gap between exposure and the point at which the test can actually pick up the infection. During that gap the pathogen is present but hasn't multiplied enough, or your body hasn't made enough antibodies, for the test to register it. Test inside that window and you can get a negative that simply isn't true yet. The test isn't broken; the infection just isn't detectable.
The window differs by infection and by which test is run, so frame the timing from your specific exposure date, not a generic chart:
- Chlamydia and gonorrhea: a NAAT is generally reliable about two weeks after exposure. If you test sooner because you're worried, that's fine — just plan to retest later, since an early negative can miss a recent infection USPSTF screening.
- HIV: the window depends entirely on the test. A nucleic acid test (NAT) can detect infection about 10 to 33 days after exposure; an antigen/antibody lab test about 18 to 45 days; and a rapid antibody test about 23 to 90 days CDC HIV testing.
- Syphilis and hepatitis: these are blood tests with their own windows, and a negative soon after exposure may need repeating.
If your exposure was very recent, or you're unsure of timing, don't guess — our guide to when to test after exposure breaks down each infection's window so you book the test on the day it can actually find something. People often test the morning after and treat the negative as an all-clear, which is a costly mistake.
Where to get tested and what it costs
You are rarely far from affordable testing. The US has roughly 16,000 federally-funded community health centers and about 4,200 Title X family-planning clinics, alongside tens of thousands of other public STI clinics — most offering free care or income-based sliding-scale fees HRSA health centers. Doctors' offices, local health departments, and Planned Parenthood all test, and at-home and self-collection kits let you swab or collect a sample at home and mail it in.
At-home kits are convenient, but mind the window — order and use one only when enough time has passed for the test to be accurate, or you've spent money on a result you'll have to repeat. If you're choosing between clinic visits and mail-in options, you can compare testing providers to weigh cost, turnaround, and which infections each panel covers.
Reading your results and how accurate they are
Modern NAATs are the most sensitive tests for chlamydia and gonorrhea, which is why guidelines recommend them, and they're highly accurate, with specificity around 99%, meaning false positives are uncommon. The far more common error is a false negative, and it almost always comes from testing before the window period is over.
To protect against false positives where the stakes are highest, HIV and syphilis use a two-step process: an initial screening test, then a different confirmatory test, and the result isn't final until the confirmatory step agrees CDC syphilis lab, 2024. A reactive rapid HIV test is a preliminary result that must be confirmed with a follow-up lab test before it means anything definitive. If a rapid test flags reactive, the next step is confirmation.
| Test | Sample | Approx. window after exposure | Confirmation needed? |
|---|---|---|---|
| Chlamydia / gonorrhea (NAAT) | Urine or swab | About 2 weeks | No — but retest if tested early |
| HIV NAT | Blood | About 10–33 days | Yes, confirm a positive |
| HIV antigen/antibody (lab) | Blood | About 18–45 days | Yes |
| HIV rapid antibody | Blood/oral fluid | About 23–90 days | Yes — reactive is preliminary |
| Syphilis | Blood | Per guidelines; two-step | Yes — confirmatory step |
If a result comes back positive
Most common STIs are curable or manageable, and treatment is usually straightforward — often a single dose or a short course. Start treatment promptly, and for chlamydia in particular, plan to retest a few months after treatment, since reinfection from an untreated partner is common; our guide on chlamydia reinfection explains why that retest matters even after you've been cured.
When to see a clinician
Book a visit if you have symptoms — discharge, burning with urination, sores, pelvic or testicular pain, unusual bleeding — even if you tested negative recently, because timing or the wrong panel can miss things. See someone too if you had a known exposure to a partner with a diagnosed STI, if you're pregnant, or if a result is positive or a rapid test is reactive and needs confirmation. Trichomonas is a frequently overlooked cause of discharge; our page on trichomoniasis testing & diagnosis covers when to ask for that specific test, since it isn't always in a default panel.