About This Calculator
The HIV Risk Calculator is a free, confidential educational tool that estimates the statistical probability of HIV transmission from a described exposure. It exists to help people move from anxiety and guesswork toward accurate, source-based information and sensible next steps such as testing or speaking with a clinician.
What the tool does
You describe an exposure (for example the type of contact, the number of exposures, and what is known about the partner). The calculator combines this with published per-act transmission probabilities and epidemiological data to produce an estimated probability range, along with general guidance on testing windows.
Where the numbers come from
The per-act transmission probabilities used here are drawn from peer-reviewed epidemiological literature and public health sources, including the U.S. Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO). Real-world risk is influenced by many factors we cannot fully capture, such as viral load, condom use, circumcision status, the presence of other sexually transmitted infections, and whether either partner is using PrEP or is virally suppressed on treatment.
What the tool is not
Why we built it
Reliable information about HIV risk is often buried in dense clinical papers or scattered across forums where the quality varies wildly. Our goal is to present the underlying statistics clearly, cite reputable sources, and always point toward testing and care rather than away from it.
Editorial approach
We aim to keep the content aligned with current CDC and WHO guidance. If you believe something is inaccurate or out of date, please tell us through the Contact page. HIV prevention science evolves, and we would rather correct an error than leave it standing.