Prevalence and per-act risk are different numbers
Two numbers decide your risk from one sexual encounter with someone whose HIV status you don’t know:
- Prevalence: the share of adults in a place who have HIV. The figures here are UNAIDS estimates for adults aged 15 to 49. For a few countries without one, such as the US, the calculator uses approximate national figures.
- Per-act risk: the chance HIV passes on in one act if your partner does have HIV and isn’t on effective treatment. For insertive vaginal sex, CDC estimates this at 0.04% (about 1 in 2,500).
Your overall risk is roughly the first multiplied by the second. That’s why the numbers in the tables below are so much smaller than the per-act risks you may have read about elsewhere.
Treatment changes the picture
A person with HIV who keeps an undetectable viral load on treatment doesn’t pass HIV on through sex. This is known as U=U. So what matters isn’t only how many people have HIV, but how many of them are on treatment and virally suppressed.
Worldwide, WHO reports that at the end of 2025 about 41.0 million people were living with HIV. Of them, 88% knew their status, 89% of those were on treatment, and 95% of those on treatment had a suppressed viral load. Coverage varies a lot between countries, and the tables take each country’s own treatment coverage into account.
Single-act risk with a partner of unknown status
Each table shows the estimated risk from one act of insertive vaginal sex without a condom (a man with a woman) with a partner whose status is unknown, using that country’s prevalence and treatment data.
The Americas
| Country | Risk per exposure | Odds |
|---|---|---|
| United States | <0.0001% | 1 in 1,500,000 |
| Canada | <0.0001% | 1 in 16,000,000 |
| Mexico | <0.0001% | 1 in 3,600,000 |
| Brazil | <0.0001% | 1 in 1,700,000 |
| Argentina | <0.0001% | 1 in 3,300,000 |
| Colombia | <0.0001% | 1 in 3,000,000 |
| Jamaica | 0.00021% | 1 in 470,000 |
| Haiti | 0.00015% | 1 in 660,000 |
Europe
| Country | Risk per exposure | Odds |
|---|---|---|
| United Kingdom | <0.0001% | 1 in 15,000,000 |
| Ireland | <0.0001% | 1 in 22,000,000 |
| France | <0.0001% | 1 in 8,000,000 |
| Germany | <0.0001% | 1 in 23,000,000 |
| Spain | <0.0001% | 1 in 15,000,000 |
| Italy | <0.0001% | 1 in 8,000,000 |
| Netherlands | <0.0001% | 1 in 39,000,000 |
| Portugal | <0.0001% | 1 in 3,600,000 |
| Poland | <0.0001% | 1 in 2,500,000 |
| Ukraine | 0.0004% | 1 in 250,000 |
| Russia | 0.00048% | 1 in 210,000 |
Asia and the Pacific
| Country | Risk per exposure | Odds |
|---|---|---|
| India | <0.0001% | 1 in 4,200,000 |
| China | <0.0001% | 1 in 2,500,000 |
| Japan | <0.0001% | 1 in 12,000,000 |
| Thailand | <0.0001% | 1 in 1,700,000 |
| Vietnam | <0.0001% | 1 in 3,500,000 |
| Philippines | <0.0001% | 1 in 9,300,000 |
| Indonesia | <0.0001% | 1 in 1,500,000 |
| Pakistan | <0.0001% | 1 in 4,200,000 |
| Australia | <0.0001% | 1 in 50,000,000 |
Africa and the Middle East
| Country | Risk per exposure | Odds |
|---|---|---|
| Egypt | <0.0001% | 1 in 12,000,000 |
| Morocco | <0.0001% | 1 in 11,000,000 |
| Nigeria | 0.00014% | 1 in 710,000 |
| Ghana | 0.00047% | 1 in 210,000 |
| Cameroon | 0.00024% | 1 in 420,000 |
| Ethiopia | <0.0001% | 1 in 1,500,000 |
| Kenya | 0.0003% | 1 in 330,000 |
| Uganda | 0.00052% | 1 in 190,000 |
| Tanzania | 0.00035% | 1 in 280,000 |
| Mozambique | 0.0014% | 1 in 70,000 |
| Zimbabwe | 0.00055% | 1 in 180,000 |
| South Africa | 0.0023% | 1 in 44,000 |
| Botswana | 0.00091% | 1 in 110,000 |
| Eswatini | 0.0014% | 1 in 69,000 |
Regional averages
| Country | Risk per exposure | Odds |
|---|---|---|
| World average | <0.0001% | 1 in 1,200,000 |
| Sub-Saharan Africa | 0.00035% | 1 in 280,000 |
| Eastern and Southern Africa | 0.00046% | 1 in 220,000 |
| Western and Central Africa | 0.00018% | 1 in 570,000 |
| Latin America and the Caribbean | <0.0001% | 1 in 1,300,000 |
| South Asia | <0.0001% | 1 in 5,300,000 |
| Middle East and North Africa | <0.0001% | 1 in 4,300,000 |
For receptive vaginal sex (a woman with a man), the per-act risk is higher. In the United States, for example, the estimate with a partner of unknown status is 0.00014% (about 1 in 730,000), and in South Africa it’s 0.0023% (about 1 in 44,000). Full tables for every type of sex are on the risk tables page.
Where HIV is most common
WHO reports that 64% of people living with HIV are in the WHO African Region. Prevalence is highest in eastern and southern Africa, where in a few countries a sizeable share of adults have HIV. In much of Western Europe, East Asia and the Middle East, it is well under one percent.
National figures are only a starting point
A country average hides big differences. HIV is more common in some cities, communities and sexual networks than others. CDC links gaps like these to social factors such as poverty, stigma and unequal access to health care. UNAIDS estimates that gay and bisexual men and other men who have sex with men are about 23 times more likely to acquire HIV, and people who inject drugs about 14 times. HIV is also far more common among sex workers and trans women than in the general population.
So for a man having receptive anal sex with another man of unknown status in the United States, the estimate is 0.05% (about 1 in 2,000), higher than the vaginal-sex figures above. The calculator lets you add these details to get a closer estimate.
What the numbers can’t tell you
These are averages. They can’t tell you whether one particular person has HIV. Anyone can have HIV without knowing, especially in the first weeks after infection, when the viral load is highest. A low number is reassuring, but only a test gives you a definite answer.
What to do now
- Exposed in the last 72 hours, with a partner who has HIV or whose status you don’t know? Ask about PEP (post-exposure prophylaxis) today. It must start within 72 hours and works best within 24. How to get PEP
- Want a definite answer? Test after the window period. The HIV test accuracy by week page shows when a negative result from each test is conclusive.
- Want a number for your situation? The calculator combines the country, the type of exposure and any protection you used.