Clinical Testing Tool

STI Window Period Calculator

Diagnostic tests need time to detect bacterial genetic material or immune antibodies. Use this STI testing window period calculator to see when each test becomes clinically conclusive.

Check your STI testing window

Diagnostic Window Period Estimator

When did the potential exposure occur?

Diagnostic tests cannot detect pathogens immediately. Select the number of days since your encounter to see which tests are reliable today and when follow-up confirmation is recommended.

Days since encounter:14 days (2 weeks, 0 days)

days

Quick Presets:

I am currently experiencing symptoms(Such as genital pain, unusual discharge, sores, burning during urination, or pelvic cramps). If symptoms are present, do not wait for window periods—book an in-person sexual health clinic appointment immediately.

Diagnostic Testing Accuracy (14 Days Post-Exposure)

Evaluated against CDC, WHO, and BASHH clinical guidelines.

Chlamydia & Gonorrhoea NAAT

Nucleic Acid Amplification (DNA)

Accurate / Conclusive

The window period has passed. A negative result today is clinically conclusive for this exposure.

Sample type: First-catch urine or self-collected vaginal / rectal / throat swab

Highly sensitive molecular test. Testing before 14 days carries a significant risk of false negative results.

HIV 4th Generation Lab Blood Test (Ag/Ab)

p24 Antigen & HIV 1/2 Antibodies (Vein blood draw)

Too Early to Test

Testing today carries a high risk of a false negative. Please test in 4 days (at day 18).

Sample type: Blood sample sent to hospital laboratory

Detects the viral p24 protein early (from 18 days) and antibodies. Conclusive at 45 days (6 weeks) per modern clinical guidelines.

HIV Rapid Self-Test / Point-of-Care

Antibody Finger-prick or Oral Fluid

Too Early to Test

Testing today carries a high risk of a false negative. Please test in 16 days (at day 30).

Sample type: Finger-prick blood or oral gum swab

Rapid screening tests detect antibodies only. Full conclusive reliability requires 90 days (12 weeks).

Syphilis Serology (EIA / RPR Blood Test)

Treponemal & Non-Treponemal Antibodies

Too Early to Test

Testing today carries a high risk of a false negative. Please test in 7 days (at day 21).

Sample type: Blood draw

Antibodies develop gradually. Earliest reliable check is 3–4 weeks; fully conclusive at 12 weeks (90 days).

Hepatitis B (HBsAg)

Surface Antigen (HBsAg)

Too Early to Test

Testing today carries a high risk of a false negative. Please test in 16 days (at day 30).

Sample type: Blood draw

Surface antigen becomes detectable around 4–6 weeks post-exposure; fully conclusive at 6 months (unless previously vaccinated).

Hepatitis C (HCV Antibody / RNA)

HCV Antibody & confirmatory RNA PCR

Too Early to Test

Testing today carries a high risk of a false negative. Please test in 46 days (at day 60).

Sample type: Blood draw

Antibodies take 8–12 weeks to develop; RNA PCR can detect earlier if clinically indicated.

Clinical Screening Guideline for Active Adults

Sexual health clinicians recommend full routine STI screening (Chlamydia, Gonorrhoea, HIV, Syphilis) every 3 to 12 months depending on your partner frequency, or whenever you change sexual partners. Many services offer free, confidential home swab/urine test kits.

Read our complete guide to STI Testing & Clinics →

How to use this STI window period calculator

Enter the date of the exposure you are worried about. The calculator returns the earliest date each test becomes reliable, counting forward from that day. If there have been several exposures, use the most recent one — that is the date that governs when a result can clear the whole period.

Why window periods differ between infections

A window period is the gap between exposure and the point a test can reliably detect an infection. It differs by infection and by test technology, which is why there is no single answer to how long after exposure to test.

HIV window period: modern combination antigen/antibody tests detect most infections earlier than antibody-only tests, but a repeat test is still standard.
Chlamydia and gonorrhoea: nucleic-acid tests look for bacterial genetic material, so they turn positive relatively early.
Syphilis: blood tests look for the immune response, which can take several weeks to develop.
Hepatitis B and C: blood tests, with windows that vary by the marker being measured.

When repeat testing is needed

A negative result taken inside the window period does not rule an infection out — it only tells you the test could not see it yet. Repeat testing at the point the window closes is the part people most often skip. If you have symptoms now, do not wait for a window to pass: get seen, because symptomatic infections are assessed differently from routine screening.