When can you test for Chlamydia? Window period and the right test

From 14 days after the sex you’re worried about. That’s Better2Know’s figure, and our Chlamydia page puts it plainly: Chlamydia can be accurately tested for 14 days after unprotected sex.

UK guidance agrees. The 2026 guideline from BASHH (the British Association for Sexual Health and HIV) recommends testing when you first come forward. If the sex was within the last two weeks, it recommends a second test two weeks after it.

In plain terms, an early test can find an infection, but only a test at 14 days or later can rule one out. Two things move the date to today: symptoms, and a partner who has told you they have Chlamydia.

Because the test needs something to find. Chlamydia is caused by a bacterium, Chlamydia trachomatis. It can settle in the urethra (the tube you pee through), the cervix (the neck of the womb), the throat or the rectum, and then multiply.

A NAAT (nucleic acid amplification test) is a laboratory test that looks for the bacterium’s genetic material in a urine sample or a swab. It copies that material until there’s enough to detect, which makes it very sensitive once an infection has taken hold.

So why might it miss Chlamydia on day three? Because in the first few days there may be too little of it to detect. The wait is biology, not red tape.

Not quite, although the two are easy to mix up. An incubation period is the time between catching an infection and noticing symptoms. A window period is the time between catching an infection and the point when a test can reliably find it.

For Chlamydia, symptoms are a poor guide either way, because most people don’t get any:

• BASHH says about half of men with Chlamydia in the urethra notice symptoms, usually 1 to 3 weeks after infection.
• The NHS says most people with Chlamydia have no symptoms at all, and when symptoms do appear, they can start anywhere from a week to several months after infection.
• UKHSA’s National Chlamydia Screening Programme estimates that around 70% to 80% of people with Chlamydia don’t know they have it.

So the window period is the number that matters, and at Better2Know it’s 14 days. Our product pages call it the “incubation period”, so don’t let the label throw you. Our guide to the difference between a window period and an incubation period explains more.

You can, and sometimes it works. A test on day three can already be positive if the bacteria are multiplying quickly. It can also come back negative in someone who is infected, simply because there isn’t enough to find yet.

An early positive counts, but an early negative isn’t the final word. If two weeks feels impossible, here’s what I’d suggest:

• Test now and again at 14 days. That’s the BASHH approach, and it’s what we often suggest to people who are anxious. The first test may give you an early answer; if it’s negative, the second is the one that counts.
• Leftover antibiotics won’t settle it. Taking them “just in case” may not treat Chlamydia properly, and it can make a later test harder to interpret.
• A partner’s diagnosis changes the timing. If someone has told you they have Chlamydia, there’s no need to wait 14 days: test now and mention it when you book.

No. Symptoms are a reason to test today, not a reason to wait. The 14-day wait is there to stop a negative result reassuring you too early, and a positive result counts whenever it comes.

The usual signs, according to the NHS:

• In men: a white, cloudy or watery discharge from the tip of the penis, burning and itching around the testicles and penis, pain and swelling in the testicles, or a burning feeling when you pee.
• In women: vaginal discharge that isn’t normal for you, bleeding after sex or between periods, pain in your lower tummy, or a burning feeling when you pee.

Our post on what Chlamydia discharge smells like goes into more detail. If that sounds like you, the symptoms row in the table below is the one to look at. One urine sample checks for Chlamydia, Gonorrhoea and five other infections that can cause discharge, itching or pain.

Severe pain low in your tummy, a high temperature or a very painful, swollen testicle need urgent medical care the same day.

The right test depends on how long it’s been and whether you have symptoms. Earliest test days and results times are from our product pages, and results times count from when your sample reaches the laboratory.

Better2Know’s booking data shows that 61% of Chlamydia test bookings at our UK clinics are for a wider screen. That makes sense, because Gonorrhoea and Syphilis can be passed on in the same encounter. One visit at 14 days tests for all three.

Does a urine sample cover oral and anal sex?

No. A urine sample doesn’t test the throat or the rectum, and BASHH notes that Chlamydia in those places usually causes no symptoms.

If you gave oral sex or received anal sex, you can add a throat swab or a rectal swab, both from 14 days. Our post on testing after unprotected oral sex looks at oral sex and STIs more widely.

What does a 14-day result tell you?

For Chlamydia and Gonorrhoea, a negative result from 14 days is one you can rely on. Syphilis is different, because antibodies can take longer to show, so after a high-risk contact BASHH recommends a repeat test 3 months later.

How does testing work?

You can test at one of hundreds of clinics across the UK or with a home test kit that arrives in plain packaging. Weekday orders placed before 4pm go out by first class post the same day.

Results go to your secure online patient area, and everything is confidential, with the option to stay completely anonymous. Weighing up a wider screen? Our guide “Which STI test do I need?” compares the options.

Two weeks is a long time to worry, and it’s normal to spend most of it doing exactly that. A plan helps:

• Work out the date. Count 14 days from the last time you were at risk; if there was more than one occasion, the clock starts at the most recent. Put the date in your phone and let it do the remembering.
• Condoms or a pause make the wait safer. If you do have Chlamydia, it can be passed on during these two weeks even though you feel fine. Condoms, or a break from sex until your result, cut that risk.
• If the result is positive, it’s treatable. Chlamydia is treated with antibiotics, and a Better2Know doctor can help you get the right medication and advice. The NHS says current and recent partners need testing too, so a word with yours now saves a harder conversation later.
• If HIV is a worry, time matters. If you think you were exposed in the last 72 hours, urgent medical care can assess you for PEP (post-exposure prophylaxis). That’s emergency HIV medication, and it has to start within that time.
• HIV testing has its own timetable. Our 28-day screen includes HIV, and after a high-risk exposure the UK HIV testing guidelines recommend repeating it once 45 days have passed.

Can I take a Chlamydia test on my period?

Yes, and your period needn’t delay it. A little blood in a urine sample shouldn’t cause much of a problem, and a lighter day gives the best sample. Heavy bleeding can occasionally affect a swab, as our post on testing during your period explains.

Should I test again after treatment?

Not usually straight away. BASHH doesn’t recommend a routine test of cure for uncomplicated Chlamydia. The exceptions are pregnancy, symptoms that persist and treatment that may not have been completed, and even then not before 3 weeks after finishing treatment.

It does recommend a retest 2 to 6 months after treatment for anyone under 25, because re-infection is common.

So the answer is a date in your diary: 14 days after the last time you were at risk. Before then a test can find Chlamydia but can’t rule it out, and symptoms or a partner’s diagnosis bring the date forward to today. Prefer to talk it through first? Our Patient Care Team is available 24/7 on 020 7099 0955.

Not in the UK? Choose your country from the selector at the top of the page for local tests and prices.

Medical review. This article was medically reviewed by Dr Steve Chapman, a doctor with a wealth of clinical experience in the field of STIs. Better2Know content is reviewed for clinical accuracy before publication and updated when guidance or surveillance data changes. It is general information and not a substitute for personal medical advice.

Sources

1. UK Health Security Agency, Sexually transmitted infections and screening for chlamydia in England: 2025 report, 2 June 2026. https://www.gov.uk/government/statistics/sexually-transmitted-infections-stis-annual-data-tables/sexually-transmitted-infections-and-screening-for-chlamydia-in-england-2025-report
2. British Association for Sexual Health and HIV, UK national guideline for the management of infection with Chlamydia trachomatis, 2026. https://www.bashh.org/_userfiles/pages/files/national_guideline_for_the_management_of_infection_chlamydia_trachomatis_2026.pdf
3. NHS, Chlamydia, page last reviewed 24 October 2024. https://www.nhs.uk/conditions/chlamydia/
4. UK Health Security Agency, National Chlamydia Screening Programme: programme overview, updated 24 June 2021. https://www.gov.uk/government/publications/ncsp-programme-overview/ncsp-programme-overview
5. British Association for Sexual Health and HIV, UK guidelines for the management of syphilis, 2024. https://www.bashh.org/_userfiles/pages/files/syphilis_2024.pdf
6. British HIV Association, British Association for Sexual Health and HIV and British Infection Association, adult HIV testing guidelines, 2020. https://www.bashh.org/_userfiles/pages/files/resources/hivtesting2020wiley.pdf
7. Better2Know UK pages for the Peace of Mind and its home test kit, Chlamydia and Gonorrhoea (Urine) and its home test kit, the Instant Chlamydia and Gonorrhoea Screen, the Comfort Screen, the Full Screen and its home test kit, the throat and rectal swab tests, the Chlamydia information page, the home page and the clinics page, checked 29 September 2026.
8. Better2Know booking data, 1 January 2025 to 31 July 2026, internal analysis (Data Register UK-05).