This page is general health information, not medical advice. It cannot tell you whether you have an infection. A clinician can, and the testing options on this site are a good place to start.

If something happened recently and you are wondering when to get tested for STDs, you are asking the right question at the right time. The answer depends on the infection, the type of test and how many days have passed.

This guide walks you through the steps in order. It uses window period numbers from the CDC, and it points to Chicago clinics where you can be tested and treated.

What a window period is

A window period is the time between an exposure and the point when a test can reliably pick up an infection. Testing inside that window can come back negative even though an infection is present. That is why timing matters.

The std window period is not the same for every infection. The HIV window period also changes with the kind of HIV test. A clinician can match the test to your dates.

Materials you will need

The date of the exposure, and any other exposures since then.
A short note on what kind of exposure it was (for example, condomless vaginal, anal or oral sex, a shared needle, or a condom that broke).
Any symptoms, with the dates they started. Our guide to STD symptoms, when to test and where can help you describe them.
An insurance card, if you have one. The Chicago Department of Public Health (CDPH) asks insured patients to bring it, and it also says care is provided regardless of ability to pay or insurance status.
A phone to call the clinic and a way to write down what you are told.

Step 1: Write down the date and what happened

Count the days from the exposure to today. This number decides almost everything that follows.

If there was more than one exposure, count from the most recent one. A clinician will usually ask about all of them.

Step 2: If it was within the last 72 hours, call about PEP now

The CDC says post-exposure prophylaxis (PEP) for HIV should be started as soon as possible, and within 72 hours of a possible exposure. It is a medicine a clinician prescribes, so it needs a visit or a call to a clinic that offers it.

Do not wait for a test result to ask about PEP. A test taken right after an exposure cannot tell you much about that exposure. PEP is a separate decision that you and a clinician make together.

In Chicago, Howard Brown Health lists PEP at its walk-in sexual health sites and says no appointment is necessary. The number is 773.388.1600. The CDPH Sexual Health Specialty Clinics list PrEP and treatment services, so call to ask whether they can see you for PEP. The Illinois HIV/STD Hotline at 1-800-243-2437 is another place to ask where to go.

The CDC also describes doxy-PEP, a 2024 option in which a clinician may prescribe an antibiotic after sex to lower the chance of some bacterial STIs. The CDC's guidance is aimed at certain groups, such as men who have sex with men and transgender women who had a bacterial STI in the past year. A clinician decides if it fits. Howard Brown offers doxy-PEP by appointment.

Step 3: Look up the window period for each infection

The table below gives the CDC's HIV test windows. Where the CDC does not publish a single fixed window, the table says so rather than guessing.

Infection or test	What the CDC says about timing
HIV, nucleic acid test (NAT)	Can usually detect HIV 10 to 33 days after exposure.
HIV, antigen/antibody test on blood from a vein	Can usually detect HIV 18 to 45 days after exposure.
HIV, rapid antigen/antibody test on a finger stick	Can usually detect HIV 18 to 90 days after exposure.
HIV, antibody test	Can usually detect HIV 23 to 90 days after exposure.
Chlamydia, gonorrhea, trichomoniasis	The CDC STI Treatment Guidelines (2021) do not set one fixed window. Ask a clinician how your dates affect testing.
Syphilis	The CDC guidelines say a person exposed to a partner with early syphilis within the previous 90 days may be treated by a clinician even before test results are reliable.
Herpes and HPV	The CDC does not recommend routine screening for people without symptoms. A clinician can explain which tests apply to you.

The CDC says that an HIV test taken before the end of its window may need to be repeated. For more detail, see the CDC page on HIV testing.

Step 4: Decide whether to test now, later or both

How soon can you test for STDs? You can be seen as soon as you want. A clinic can also test for symptoms, and talk through your exposure, at any time.

What changes with timing is how much a negative result can tell you. Early in the window, a negative result may not be the final word. That is why many clinicians suggest testing now and again later.

Test now if you have symptoms, if you are worried, or if you want a baseline. It can also catch an infection from an earlier exposure.
Test again later once the window for the infection has passed. For HIV, that means the end of the window for the test your clinic uses.
Ask about a partner's diagnosis. If a partner tells you they have a diagnosed infection, tell the clinician. They may treat you or advise on next steps without waiting for results.

Step 5: Pick the test that matches your dates

Ask the clinic which HIV test it uses. A lab antigen/antibody test on blood from a vein has a shorter window than an antibody-only test. A nucleic acid test has the shortest, according to the CDC, and is used in specific situations.

Your dates may fall between two windows. A clinician can say what a result would and would not tell you, and when to come back.

Step 6: Choose where to go in Chicago

Several places in the city offer testing and treatment, and some take walk-ins. Our list of Chicago testing locations has the full picture, and our guide to STD testing in Chicago and what it costs goes deeper on costs. Here are the main options.

CDPH Sexual Health Specialty Clinics. There are three: Lakeview (2849 N. Clark St., 312.744.5507), Austin (4909 W. Division St., Suite 411, 312.746.4871) and Roseland (200 E. 115th St., 312.747.1090). CDPH says to call for an appointment, that limited walk-ins are available, and that the clinics are closed 12 to 1 pm daily and on City holidays. Hours differ by clinic, so call to verify. See the CDPH sexual health page.
Ruth M. Rothstein CORE Center (Cook County Health). 2020 W. Harrison St. The Cook County Health page says to call the walk-in STI Screening Clinic Monday to Friday, 8:30 am to 3:30 pm, and that same-day HIV and STI services are provided. The number is 312-572-4700. The CDC GetTested listing shows a sliding scale.
Howard Brown Health. Walk-in sexual health care with no appointment necessary, first come, first served, at Sheridan (4025 N. Sheridan Rd.), 63rd St. (641 W. 63rd St.) and the Broadway Youth Center (1023 W. Irving Park Road). The phone is 773.388.1600. Howard Brown describes the service as low-cost and offers a sliding fee program based on income and family size.
Planned Parenthood of Illinois, Rogers Park. 5725 N Broadway, (773) 942-7193. The CDC GetTested listing says an appointment is required.

Prices are not published on every page. CDPH does not say its visits are free, so ask about cost when you call. You can also search the CDC's GetTested locator by ZIP code.

Young people can get care on their own. Under Illinois law (410 ILCS 210/4), a minor 12 or older who may have come into contact with an STD can consent to prevention, diagnosis or treatment services without a parent. Providers must report each STD incident to public health, and they may make reasonable efforts to involve family if they believe it will not be harmful.

Step 7: Get ready for the visit

Call first, even for a walk-in site, to confirm hours and ask about cost.
Say the date of your last exposure at the start of the visit.
Ask which tests will be done and which infections they cover.
Ask when a repeat test would be useful, and write the date down.
Ask how and when you will get your results.

Tell the clinician about every kind of sex you have had, because tests can be taken from different sites. They will not judge. This is routine information for them.

Step 8: Look after yourself and your partners while you wait

While you wait for the window to pass, a clinician can tell you how to lower the chance of passing anything on. Condoms and avoiding sex until you have a result are common suggestions. Treatment can be started as soon as a diagnosis is made.

If a clinician diagnoses chlamydia, gonorrhea or trichomoniasis, Illinois allows expedited partner therapy (EPT). According to the CDC's legal status page for Illinois, this lets a clinician provide treatment for partners exposed in the previous 60 days. It does not cover syphilis. Ask whether it applies to you.

In Illinois, HIV, syphilis, gonorrhea and chlamydia are reportable. Clinicians report to public health, and in Chicago that is the health department. This is a standard step. It is part of how the city tracks and responds to infections.

Tips and common mistakes to avoid

Treating one early negative as the final answer. A negative taken inside the window may need to be repeated.
Waiting to ask about PEP. The 72-hour mark passes quickly, so call the same day.
Skipping the retest. After treatment for chlamydia, gonorrhea or trichomoniasis, the CDC recommends retesting about three months later because repeat infection is common.
Assuming no symptoms means no infection. Many STIs cause no symptoms, which is why the CDC and USPSTF recommend screening for some groups.
Not mentioning a new exposure. A new exposure can restart the clock for some tests.
Going alone to a closed clinic. Call first, because hours and walk-in rules change.

What results can mean

A negative result after the full window has passed may mean no infection was detected. A negative result before the window ends may not rule out an infection, which is why a repeat test can help. A positive result is something a clinician will talk through with you.

Bacterial STIs and trichomoniasis can be cured with treatment from a clinician. HIV and herpes are not curable, but they are treatable and manageable. HPV often clears on its own, and a clinician can explain screening and vaccination.

Chlamydia and gonorrhea are common in the city. IDPH reported a 2022 chlamydia rate of 1,023.7 per 100,000 people in Chicago, and a gonorrhea rate of 459.3 per 100,000. These are infections clinicians treat every day.

Where to go next

If you are inside 72 hours, call a PEP-capable clinic today. If you are past that, pick a clinic from the steps above, test when you are ready, and plan a repeat for the end of the window.

Free and low-cost testing is available in Chicago. The CDC's GetTested tool and the Illinois HIV/STD Hotline at 1-800-243-2437 can help you find a place.

When to Get Tested After Exposure: STD Window Periods Explained