You’ve had unprotected sex. Maybe the condom broke, maybe things just happened, or maybe you’re not sure if your partner has been tested. The responsible thing to do is get tested, right?
Here’s the thing: if you rush to get tested the day after (or even the week after) unprotected sex, there’s a high chance the test won’t pick up an infection even if you did get something.
That’s because of something called a window period.
What Is a Window Period?
A window period is the time between when you’re exposed to an STI and when it will actually show up on a test. During this time, the infection might be in your body, but your immune system hasn’t produced enough antibodies yet, or there isn’t enough of the bacteria or virus for the test to detect.
According to Brook, if you get tested too soon after exposure, the results might be negative even if you’re infected. Testing too early is one of the most common reasons people get inaccurate results.
Window Period vs. Incubation Period
These are two different things, and it’s easy to mix them up:
Window period: The time between exposure and when a test can detect the infection.
Incubation period: The time between exposure and when symptoms appear.
Here’s the catch: most STIs don’t cause symptoms at all. Many people with chlamydia and gonorrhoea have no symptoms. So waiting for symptoms to appear before getting tested isn’t a reliable strategy.
Window Periods for Common STIs
Different STIs have different window periods. Here’s when you should get tested after potential exposure, according to Brook and NHS guidance.
Chlamydia
Window period: 2 weeks
Brook recommends waiting at least 2 weeks after unprotected sex before testing for chlamydia. Tests look for the bacteria itself, not antibodies, so they can detect it relatively quickly.
If you test earlier and get a negative result, you should retest after the 2-week mark if you had potential exposure.
Gonorrhoea
Window period: 2 weeks
Like chlamydia, Brook advises waiting 2 weeks after potential exposure before testing for gonorrhoea. Tests detect the bacteria directly.
Gonorrhoea can develop antibiotic resistance, so accurate testing and proper treatment are crucial.
HIV
Window period: 7 weeks (45 days)
Brook and NHS services recommend waiting 7 weeks (45 days) after potential exposure before testing for HIV using modern 4th generation tests.
If you’ve had high-risk exposure, the NHS may recommend testing at 7 weeks and retesting for complete accuracy. Post-exposure prophylaxis (PEP) is also available within 72 hours of exposure if you think you may have been exposed to HIV.
Syphilis
Window period: 12 weeks (3 months)
Brook recommends waiting 12 weeks after potential exposure before testing for syphilis. Syphilis tests look for antibodies, which your body takes time to produce.
Early detection is important because untreated syphilis can cause serious health complications.
Hepatitis B
Window period: 12 weeks (3 months)
The NHS recommends waiting at least 12 weeks after potential exposure before testing for hepatitis B. The infection can take this long to show up on blood tests.
Vaccination is available for hepatitis B and is recommended for people at higher risk of exposure.
Hepatitis C
Window period: Up to 6 months
According to the NHS, hepatitis C can take up to 6 months to show up on blood tests. Testing is usually recommended at 3 months and again at 6 months after potential exposure.
There’s currently no vaccine for hepatitis C, but it’s curable with antiviral treatment.
What About Other STIs?
You might have heard about other STIs like herpes, trichomoniasis, or mycoplasma genitalium. Here’s why these aren’t included in routine STI screening:
Herpes (HSV)
The NHS explicitly states that there is no routine screening test for herpes. Herpes is only tested when you have visible symptoms (blisters, sores, or ulcers).
If you have symptoms, a healthcare provider will take a swab from the affected area during an outbreak. Blood tests for herpes antibodies aren’t routinely offered because many people have antibodies without ever having symptoms, and the test can’t tell you where the infection is located (oral or genital).
If you’re concerned about herpes, speak to a sexual health clinic – but testing is only done if you have symptoms.
Trichomoniasis
Trichomoniasis is not part of routine home testing kits offered by Brook or most NHS services. However, sexual health clinics can test for it if you have symptoms like unusual discharge or irritation.
If you have symptoms, visit a sexual health clinic in person rather than ordering a home test kit.
Mycoplasma Genitalium
Mycoplasma genitalium is only tested when you have symptoms or when you have persistent symptoms after being treated for other STIs like chlamydia or gonorrhoea.
The NHS doesn’t include this in routine screening because it’s not as common, treatment options are limited, and antibiotic resistance is a growing problem. Testing is reserved for people with specific symptoms.
What About HPV?
Human papillomavirus (HPV) is different from other STIs. There’s no routine blood test or STI screening for HPV. Instead, HPV is detected through:
- Cervical screening (smear tests): Available to people with a cervix aged 25-64 in the UK
- Anal screening: Sometimes offered to people at higher risk, including men who have sex with men, trans women, and anyone who engages in receptive anal sex
HPV is incredibly common – the NHS estimates that about 8 in 10 people will have HPV at some point in their lives. Most HPV infections clear on their own without causing problems.
Why Getting Tested Too Early Is a Problem
Testing before the window period ends can give you a false sense of security. You might get a negative result, assume you’re fine, and continue having unprotected sex – potentially spreading an infection you don’t know you have.
Brook emphasises that testing too early is one of the most common mistakes people make when it comes to sexual health. If you’ve had unprotected sex and you’re worried, it’s better to:
- Wait for the appropriate window period before testing
- Use condoms or abstain from sex in the meantime
- Consider retesting after the full window period if you’re still concerned
When Should You Get Tested?
Brook and the NHS recommend getting tested for STIs:
- After unprotected sex: Wait for the appropriate window period (2 weeks for chlamydia and gonorrhoea, 7 weeks for HIV, 12 weeks for syphilis and hepatitis B)
- After a condom breaks or slips off: Same as above
- With a new sexual partner: Ideally before having sex, but definitely within the appropriate window period
- Regularly if you’re sexually active: Annual testing is recommended, or more frequently if you have multiple partners
- If you have symptoms: Get tested immediately, even if it’s before the window period – but you may need to retest later for complete accuracy
What If You Can’t Wait for the Window Period?
If you’ve had high-risk exposure and you’re experiencing symptoms, don’t wait for the window period to end. Book an appointment with a sexual health clinic or your GP straight away.
For HIV specifically, if you’ve had very high-risk exposure (like unprotected sex with someone who is HIV-positive or sharing needles), you may be eligible for post-exposure prophylaxis (PEP). This must be started within 72 hours of exposure and can prevent HIV infection. Contact a sexual health clinic or A&E immediately if you think you need PEP.
Where to Get Tested
United Kingdom
STI testing is free and confidential on the NHS. You can:
- Order a home testing kit: Visit sh24.org.uk or your local sexual health service website
- Visit a sexual health clinic: Find your nearest clinic at nhs.uk/service-search/sexual-health
- See your GP: Though they may refer you to a specialist clinic
- Visit Brook: If you’re under 25, Brook offers free, confidential sexual health services at brook.org.uk
United States
STI testing options in the US vary by location and insurance coverage:
- Planned Parenthood: Offers affordable STI testing at clinics nationwide. Find your nearest location at plannedparenthood.org
- Local health departments: Many offer free or low-cost testing. Search by zip code at gettested.cdc.gov
- Your healthcare provider: Most insurance plans cover STI screening
- Community health centers: Offer sliding scale fees based on income
- At-home testing kits: Available through services like Nurx, MyLAB Box, and LetsGetChecked (paid options)
Canada
STI testing is covered by provincial health plans:
- Sexual health clinics: Free and confidential testing available in most provinces
- Your family doctor: Can order STI tests covered by provincial health insurance
- Walk-in clinics: Most offer STI testing services
- Find services: Visit sexandu.ca for clinic locator
Australia
STI testing is often bulk-billed (free) through Medicare:
- Your GP: Can order STI tests usually covered by Medicare
- Sexual health clinics: Free or low-cost testing available. Find clinics at health.gov.au
- Family Planning clinics: Offer comprehensive sexual health services
- Better2Know: Private testing service with clinics across Australia
New Zealand
STI testing is free or low-cost through public health services:
- Your GP: Most STI tests are free or subsidised
- Sexual health clinics: Free testing available at public clinics
- Family Planning: Offers confidential sexual health services at familyplanning.org.nz
Rest of World
If you’re outside these countries:
- Search for sexual health clinics in your city or region
- Check with your national health service for free or subsidised testing
- Contact international organisations: Marie Stopes International and International Planned Parenthood Federation operate in many countries
- University health services: If you’re a student, your campus health center likely offers testing
- Private labs and clinics: Available in most major cities worldwide
Remember: STI testing should always be confidential, and many services offer anonymous testing options.
Final Thoughts
Window periods exist because tests need time to detect infections. It’s frustrating to wait, especially if you’re worried, but testing too early can give you inaccurate results.
Remember: getting an STI doesn’t mean you’ve done anything wrong. It’s incredibly common, and most infections are easily treatable. The most important thing is to get tested at the right time so you can get accurate results and proper treatment if needed.
If you’re ever unsure about when to test or what to do after unprotected sex, contact a sexual health service. They’re there to help, not to judge.
References
Brook (2025). Order a test kit through SH:24: Don’t test too soon – understanding window periods. Available at: https://www.brook.org.uk/service-unavailable/
NHS Inform (2025). STI testing at home. Available at: https://www.nhsinform.scot/care-support-and-rights/nhs-services/sexual-health/sti-testing-at-home/
NHS Inform (2025). Genital herpes. Available at: https://www.nhsinform.scot/illnesses-and-conditions/sexual-and-reproductive/genital-herpes/
South Tees Hospitals NHS Foundation Trust (2024). Routine HIV, hepatitis B and C and syphilis testing. Available at: https://www.southtees.nhs.uk/services/accident-and-emergency/routine-hiv-hepatitis-b-and-c-and-syphilis-testing/
The Rotherham NHS Foundation Trust. Home testing kits. Available at: https://www.therotherhamft.nhs.uk/services/sexual-health-services/home-testing
