HIV Risk Calculator: Per-Act Transmission Estimator
| Exposure Type | Estimated Risk per 10,000 Exposures | “1 in X” Probability |
| Receptive Anal Intercourse | 138 | 1 in 72 |
| Insertive Anal Intercourse | 11 | 1 in 909 |
| Receptive Vaginal Intercourse | 8 | 1 in 1,250 |
| Insertive Vaginal Intercourse | 4 | 1 in 2,500 |
| Oral Sex (Receiving or Giving) | Low to Negligible | — |
Understanding the Probabilities
The likelihood of a viral transfer isn’t uniform; it fluctuates based on the specific nature of the contact and the biological vulnerabilities involved. Researchers have spent decades tracking these data points to provide a clearer picture of how specific actions correlate with acquisition rates.
Factors That Influence Outcomes
Viral Load: The concentration of the virus in a partner’s system is the most significant variable. When the load is undetectable, the likelihood of transfer effectively drops to zero.
Biological Barriers: Physical protection acts as a high-efficiency shield, drastically reducing the figures across all categories.
Presence of Other Pathogens: If another infection is present, the localized inflammation can increase the vulnerability of the tissue, making it easier for a virus to take hold.
Type of Exposure: Certain tissues are more vascular and delicate than others, leading to higher statistical figures for certain types of physical engagement compared to others.
