HIV Risk Calculator

Private · Free · Based on CDC & UNAIDS data

Worried about a possible exposure? Get a clear-eyed number.

Describe what happened and see the estimated chance of HIV transmission, what's driving it, and exactly when each test can give you an answer. Nothing you enter leaves your device.

The people involved

We ask about anatomy rather than gender because it determines which exposures are possible.

Your body
Their body

What happened

Used for PEP timing and test windows

Sexual contact

Choose both bodies above to see the options.

Blood or needles
Other contact

Their HIV status

For a needle or blood exposure, this is the person the blood came from.

Does the other person have HIV?

HIV prevention medication

HIV test results

Optional. Add tests taken since the exposure to refine the estimate.

Prevalence: UNAIDS estimates via World Bank indicator SH.DYN.AIDS.ZS (adults 15-49).

How it works

Three numbers, multiplied

  1. Per-act risk. How often a single act passes HIV on when the other person has HIV and isn't on effective treatment. These come from CDC estimates.
  2. Their chance of having HIV. 100% if you know they're positive. If you don't know, how common HIV is where they're from, adjusted for their sex, their community, groups with higher rates, and how many people there are on treatment.
  3. What changed the odds. Condoms, PrEP, PEP, viral load, STIs, repeat exposures, and any negative tests since.

Full details, including every figure and assumption, are on the methodology page.

Official resources

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Prevention

Worldwide