References UK clinical guidance from the NHS, the British HIV Association (BHIVA), and the British Association for Sexual Health and HIV (BASHH). Last updated: April 2026.
Every STI has its own window period — the time between exposure and when testing becomes reliable. Testing too early can miss infections that are still developing. Testing at the right time gives you accurate results and peace of mind. Here’s a clear guide to when to test for the most common STIs.
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Window Periods by Infection
| STI | Earliest Reliable Test | Definitive Test |
|---|---|---|
| Chlamydia | 1-2 weeks after exposure | 2 weeks |
| Gonorrhoea | 1-2 weeks | 2 weeks |
| HIV (4th-gen lab test) | 4 weeks | 6 weeks |
| HIV (rapid self-test) | 4 weeks (less reliable early) | 3 months |
| Syphilis | 3 weeks | 12 weeks |
| Hepatitis B | 6 weeks | 3 months |
| Hepatitis C | 6 weeks | 3 months |
| Trichomoniasis | 1-2 weeks | 4 weeks |
| Herpes (if symptoms) | Immediately — swab the lesion | Within days of lesion appearing |
| Mycoplasma genitalium | 2-3 weeks | 4 weeks |
Why Window Periods Exist
Tests look for either the infection itself (bacteria, virus) or the body’s response to it (antibodies). Both take time to develop after exposure. Testing before these reach detectable levels gives false negatives.
Urgent Testing and PEP
If you’ve had a recent high-risk exposure to HIV (within 72 hours), don’t wait for normal testing — go to a sexual health clinic or A&E about PEP. PEP is a 28-day course of medication that can prevent HIV if started promptly.
If You Have Symptoms
If you have symptoms, don’t wait. Symptoms like unusual discharge, sores, lumps, pain on urination or genital itching warrant immediate testing regardless of when you were exposed. Some infections can be detected earlier when symptoms are present.
Comprehensive Testing Strategy
After a risky exposure, a good strategy is:
- Within 72 hours — consider PEP for HIV if high risk
- 2-3 weeks — first test for chlamydia, gonorrhoea, mycoplasma
- 4-6 weeks — HIV 4th-gen test, syphilis
- 3 months — final HIV test, hepatitis B and C
Home Testing vs Clinic Testing
- Home tests are convenient and accurate when taken at the right time
- Clinic testing may offer earlier detection for some infections
- Symptoms warrant clinic assessment rather than home testing alone
- After a significant exposure, clinic testing is often the best choice
Read more: HIV window period | Home STI tests | PrEP and PEP
Frequently Asked Questions
Can I test the day after unprotected sex?
No. Testing within hours or days of exposure gives unreliable results. Wait at least 1-2 weeks for chlamydia and gonorrhoea; longer for HIV and syphilis.
Do I need to test again at 3 months if my earlier tests were negative?
A 4-6 week 4th-generation HIV test is usually sufficient. Some services offer a 3-month confirmatory test for extra reassurance, particularly after high-risk exposure.
What if I can’t wait weeks for results?
Speak to a sexual health clinic. They can discuss PEP, rapid testing options and timeframes that suit your situation.
Related reading
- Blood Test for Syphilis, Hepatitis B and Hepatitis C
- Can You Have Chlamydia and Test Negative?
- Can You Test for STIs While on Your Period?
- Hepatitis B Core Antibody Test Explained
- Hepatitis B Test Kits: What to Know
Sources
- NHS — Sexual health conditions
- BASHH — UK clinical guidelines for STI management
- British HIV Association (BHIVA) — HIV treatment guidelines
- Terrence Higgins Trust — sexual health information
- UK Health Security Agency — STI surveillance data
Steve Page is a recognised expert on Sexually Transmitted Diseases (STDs) and STD treatments, having published numerous articles in peer-reviewed journals and presented his research at conferences around the world. He has an in-depth understanding of the latest medical research on STDs, and is an advocate for the development of new treatments and protocols to improve the health of those affected. In addition to his research, he has dedicated his career to understanding the causes and symptoms of STDs, as well as how to best treat those impacted.
