HIV Risk Assessment
Select an exposure route to see CDC-estimated per-act HIV transmission probability and risk-reduction options.
Use the HIV Risk Assessment
Educational reference only. Data from CDC per-act transmission estimates. Figures are population averages — individual risk depends on viral load, STI status, and other factors. Not a substitute for HIV testing or clinical advice.
Select an exposure route
Exposure route
Per-act probability
Risk tier
Clinical context
Risk-reduction options
Recent high-risk exposure? PEP (post-exposure prophylaxis) must be started within 72 hours. Go to an emergency room or urgent care clinic now.
All routes at a glance
| Exposure route | Per-act probability | Tier |
|---|---|---|
| Receptive anal intercourse (no condom) | 1 in 72 | highest |
| Insertive anal intercourse (no condom) | 1 in 909 | high |
| Receptive vaginal intercourse (no condom) | 1 in 1,250 | moderate |
| Insertive vaginal intercourse (no condom) | 1 in 2,500 | moderate |
| Receptive oral sex (fellatio) | 1 in 10,000 | low |
| Sharing injection needles (IDU) | 1 in 160 | highest |
| Needlestick injury (healthcare) | 1 in 435 | high |
| Blood transfusion (untested blood) | ~93 in 100 | highest |
| Mother-to-child (without intervention) | ~1 in 4 | highest |
| Kissing / saliva contact | Negligible | negligible |
| Casual / household contact | Zero | negligible |
Source: CDC.gov — HIV Transmission per-act risk estimates. "Negligible" and "Zero" routes have no documented transmission cases.
Summary
This tool presents CDC-published per-act HIV transmission probabilities for common exposure routes, from receptive anal intercourse to needle sharing and blood transfusion. Select a route to see the estimated risk figure, key biological factors that raise or lower that risk, and the prevention strategies (condoms, PrEP, treatment as prevention) that apply. All figures are educational estimates — they are not diagnostic and do not replace clinical evaluation.
How it works
- Select the exposure route that applies to your situation.
- Review the CDC-estimated per-act transmission probability.
- Read the risk-reduction options shown for that route.
- Use the comparison table to see risk across all routes at once.
- Consult a healthcare provider for personal medical advice.
Use cases
- Understand relative transmission risk before speaking with a clinician.
- Compare risk levels across different exposure types.
- Learn which prevention methods apply to each route.
- Support sexual-health education and counseling sessions.
- Reference CDC probability data without navigating lengthy reports.
- Inform decisions about PEP (post-exposure prophylaxis) urgency.