Testing too early gives a false negative. Each STI has a specific window period — the time between exposure and when a test can detect infection. Here's the chart you actually need.

STI Testing Window Periods — When Can You Actually Test?

If you've had a possible exposure to an STI and you're about to get tested, timing matters. Test too early and you get a false-negative — the infection is there but hasn't built up enough to show. Test too late and you've spent weeks worrying for no reason.

Each STI has a specific window period — the time between exposure and when a test can reliably detect the infection. Here's the chart you need.

At-a-glance summary

STI	Test type	Window from exposure
HIV	4th-gen Ag/Ab blood test	18-45 days (detect by 6 weeks in most)
HIV	Rapid antibody (oral or finger)	30-90 days
HIV	RNA / NAT test	10-33 days
Chlamydia	Urine NAAT or swab	7-14 days
Gonorrhea	Urine NAAT or swab	7-14 days
Syphilis	RPR / VDRL blood test	3-6 weeks (after primary chancre)
Hepatitis B	HBsAg blood test	1-9 weeks
Hepatitis C	HCV antibody	2-26 weeks (most by 11)
HSV (herpes) — swab from lesion	PCR / culture	While lesion is active
HSV (herpes) — blood IgG	Blood test	12-16 weeks for reliable seroconversion
HPV	Cervical sample (Pap/HPV co-test)	When clinically indicated
Trichomonas	NAAT or wet mount	2-4 weeks
Mycoplasma genitalium	NAAT	2-3 weeks

HIV — the most-asked window period

HIV testing technology has improved enormously over the past 20 years. There are three test types with different windows:

4th-generation antigen/antibody test (most common)

Tests for both HIV antibodies AND p24 antigen (a viral protein that appears before antibodies). Window: 18-45 days, with most people detectable by 6 weeks. CDC recommends a follow-up at 90 days to be definitive.

Rapid HIV test (OraQuick, oral swab, or finger-stick)

Tests for antibodies only. Window: 30-90 days, longer because antibodies take time to develop. The 20-minute rapid result is convenient but less sensitive in early infection.

RNA / NAT test (HIV viral load)

Detects viral RNA directly. The fastest window: 10-33 days. Used in specific scenarios (PEP follow-up, suspected acute HIV, blood-bank screening). Expensive; not routine.

Practical recommendation:

After possible exposure: 4th-gen test at 4-6 weeks (likely detects), repeat at 12 weeks for definitive negative
If anxious and want earliest: RNA at 2-3 weeks (then 4th-gen at 4-6 weeks to confirm)
Always finish the testing sequence even if early test is negative

Chlamydia and Gonorrhea — relatively short windows

Both are detected by NAAT (nucleic acid amplification test) — extremely sensitive direct-detection of bacterial DNA. Window: 7-14 days.

Urine test (men) or self-swab (women)
Rectal and throat swabs available for site-specific exposure
Results in 2-7 days

If your exposure was less than 7 days ago, wait. Test at 2 weeks.

Syphilis — depends on stage

Syphilis testing has two phases of detectability:

Primary syphilis (chancre present, week 0-12)

Darkfield microscopy or PCR of the chancre — diagnostic immediately
Blood tests (RPR/VDRL) — may not be positive yet for the first 3-6 weeks
A negative blood test with a visible chancre doesn't rule out syphilis — get the chancre swabbed

Secondary syphilis and later (4+ weeks)

Blood tests very reliable
RPR and treponemal tests both positive

Practical: test blood at 6 weeks post-exposure. If chancre is present earlier, swab it.

Hepatitis B — relatively long window

HBV surface antigen (HBsAg) appears in the blood 1-9 weeks after exposure. Most people seroconvert by 4-6 weeks. Vaccination eliminates infection risk; if you're not vaccinated and have a high-risk exposure, Hepatitis B Immune Globulin (HBIG) + vaccine within 24 hours is preventive.

Practical: test at 6-12 weeks if unvaccinated. Get vaccinated if not already done.

Hepatitis C — longest window

HCV antibody appears 2-26 weeks after exposure (median around 11 weeks). HCV RNA appears earlier — 1-3 weeks — but is more expensive. For routine post-exposure testing, the antibody test at 12+ weeks is sufficient.

Modern direct-acting antivirals can cure hepatitis C in 8-12 weeks. Don't avoid testing because of stigma; treatment is now straightforward.

Herpes (HSV) — two paths

Active outbreak — swab the lesion

PCR or culture of a visible lesion gives a definitive answer. This is the gold standard for diagnosis.

No lesion — blood test

IgG seroconversion takes 12-16 weeks after exposure. Testing earlier than 12 weeks risks false-negative (infection present but antibodies not yet developed).

Important caveat: HSV blood tests have a meaningful false-positive rate at low-positive index values. A positive HSV-2 IgG at index 1.10-3.50 is uncertain — confirm with Western blot. See our HSV test results guide for the full picture.

CDC does NOT recommend routine HSV blood testing for asymptomatic people. Get tested if you have specific reason — symptoms, known exposure, prepregnancy planning.

HPV — different question entirely

HPV "testing" works differently than other STIs:

For women

Pap test + HPV test together (co-test) every 5 years from age 30 (3 years from age 21)
Detects cervical cell changes + presence of high-risk HPV strains
Not symptom-triggered — routine screening

For men

No FDA-approved routine HPV test
Clinical diagnosis by visible warts
Anal HPV testing available for high-risk groups (HIV+ MSM, immunocompromised)

There's no "window period" in the traditional sense for HPV — it's about screening at the right interval rather than catching a single exposure.

Trichomonas

NAAT detects within 2-4 weeks of exposure. Wet mount (microscopy) less sensitive but immediate.

Mycoplasma genitalium

Less commonly tested. NAAT window: 2-3 weeks. Tested when chlamydia/gonorrhea negative but symptoms persist.

When to test — practical sequencing

Most efficient sequence after a possible exposure:

Immediately: Decide on PEP for HIV if within 72 hours (talk to ER or sexual-health clinic). Don't wait for a test result.
2 weeks: Test for chlamydia and gonorrhea.
4-6 weeks: Test for HIV (4th-gen), syphilis, hepatitis B, and trichomonas.
12 weeks: Repeat HIV (definitive negative), HSV blood test if relevant, hepatitis C.
6 months: Repeat HIV for high-risk exposures (rare additional yield, but standard in some clinics).

Where to test

Free / sliding-scale: County STI clinic, Planned Parenthood, AHF testing centers
At-home: TakeMeHome.org (free HIV self-test), LetsGetChecked, Everlywell
Insurance-covered: Primary care visit

See our full free STI testing guide for the comparison.

What about repeat testing for ongoing risk?

For people with ongoing exposure (PrEP users, MSM with multiple partners, people who inject drugs), CDC recommends:

HIV every 3 months
Syphilis, chlamydia, gonorrhea every 3-6 months
Hepatitis B and C annually if not vaccinated / cured

Routine, not exposure-triggered.

A note on testing while symptomatic

If you have symptoms (visible sore, discharge, painful urination, rash), don't wait for the window period. Get evaluated immediately. The clinician will likely do direct testing (swab) which doesn't rely on antibody timing.

Bottom line

After a possible exposure:

HIV: 4-6 weeks for 4th-gen test, confirm at 12 weeks
Chlamydia/gonorrhea: 2 weeks
Syphilis: 6 weeks
Hepatitis B (if unvaccinated): 6-12 weeks (also consider HBIG within 24 hours)
Hepatitis C: 12 weeks (or RNA earlier if available)
HSV: only test if symptoms or specific reason; 12-16 weeks for blood IgG

Don't test too early — false negatives are worse than waiting. But also don't put it off forever. Two-thirds of STIs are silent; testing is the only way to know.

For where to get tested, see free STI testing. For after a possible exposure, see condom broke 72-hour action plan.