Having sex without a condom exposes you to two main risks: pregnancy and sexually transmitted infections. The actual likelihood of either depends on timing, the type of sex, and whether your partner carries an infection. Here’s what you need to know about both risks and the steps you can take right now.
Pregnancy Risk Depends on Timing
If penis-in-vagina sex occurred without a condom or other contraception, the chance of pregnancy varies dramatically based on where the menstrual cycle falls. The highest-risk day is around day 13 of a 28-day cycle (just before ovulation), where the probability from a single act of unprotected sex is roughly 9.7%. During the first few days of the cycle or the last few, the odds drop below 1%.
A useful rule of thumb: there’s about a 25% chance that any single act of unprotected intercourse lands within the fertile window, meaning the five days before ovulation through the day of ovulation itself. Outside that window, sperm either arrive too early and die before an egg is released, or arrive after the egg is no longer viable. But cycles aren’t always predictable, so if you’re not trying to conceive, treating any unprotected encounter as a potential pregnancy risk is the safer assumption.
Emergency Contraception Options
If pregnancy is a concern, emergency contraception is most effective the sooner you take it, but works up to 120 hours (5 days) after unprotected sex.
- Levonorgestrel pills (sold over the counter as Plan B and generics) bring the pregnancy rate down to about 1.2% to 2.1% when taken within that window. Effectiveness drops with each passing day.
- Ulipristal acetate (sold by prescription as ella) has a pregnancy rate of about 1.2% and holds its effectiveness better than levonorgestrel in the 72-to-120-hour range.
- Copper IUD is the most effective option. When inserted by a provider within 5 days of unprotected sex, it prevents pregnancy more than 99% of the time. It also doubles as long-term contraception going forward.
All three options work primarily by delaying or preventing ovulation, not by ending an existing pregnancy. The copper IUD also creates an environment that’s inhospitable to sperm.
STI Risk From a Single Encounter
Sexually transmitted infections don’t require multiple exposures. A single act of condomless sex can transmit chlamydia, gonorrhea, syphilis, HIV, herpes, HPV, hepatitis B, and trichomoniasis. Your actual risk depends on what type of sex occurred and whether your partner has an infection.
For HIV specifically, the per-act transmission risk from an infected partner varies by type of sex. Receptive anal sex carries the highest risk at about 1.4% per exposure (roughly 1 in 71). Receptive vaginal sex is lower at about 0.08% (1 in 1,250), and insertive vaginal sex is about 0.04% (1 in 2,500). Oral sex carries a low but non-zero risk. These numbers assume no condom use and a partner who is HIV-positive but not on treatment. Other factors like the presence of other STIs, genital sores, or a high viral load can increase the risk substantially.
Bacterial infections like chlamydia and gonorrhea transmit more easily than HIV per encounter. What makes them particularly tricky is that most infections produce no symptoms at all. Studies show roughly 61% of chlamydia infections, 53% of gonorrhea infections, and 57% of trichomoniasis infections in women are completely asymptomatic. Men can also carry these infections without knowing. This means you can’t rely on feeling fine as evidence that nothing was transmitted.
If You’re Concerned About HIV
Post-exposure prophylaxis (PEP) is a 28-day course of antiviral medication that can prevent HIV infection after a potential exposure. To be effective, it needs to be started within 72 hours, and the sooner the better. After 72 hours, PEP is no longer recommended because the window of effectiveness has closed.
PEP is available through emergency rooms, urgent care clinics, and sexual health clinics. If you believe there’s a realistic chance your partner could be HIV-positive, getting evaluated quickly matters more than waiting to see if symptoms appear.
When to Get Tested
Testing too early after exposure can produce a false negative because infections need time to become detectable. Each STI has its own window period:
- HIV (blood test): detectable in most cases by 2 weeks, catches nearly all infections by 6 weeks. An oral swab test takes longer: 1 month for most cases, 3 months for almost all.
- Syphilis: blood tests pick up most infections at 1 month, with 3 months needed to catch almost all cases.
- Hepatitis B: blood tests are reliable at 3 to 6 weeks.
- Chlamydia and gonorrhea: urine tests or swabs can typically detect these within 1 to 2 weeks after exposure.
If you’ve never been vaccinated for hepatitis B and you’re concerned about exposure, starting the vaccine series as soon as possible (ideally within 24 hours) can still offer protection. Your provider may also give you a dose of hepatitis B immune globulin alongside the vaccine for more immediate coverage.
What Not to Do Afterward
Douching after unprotected sex does not reduce your risk of pregnancy or infection, and it actively makes things worse. Douching strips away the vagina’s normal protective bacteria, which can allow infectious organisms to take hold more easily. It can also push pathogens upward past the cervix into the uterus and fallopian tubes, increasing the risk of pelvic inflammatory disease. If you notice unusual discharge after unprotected sex, leave it alone and see a provider, since washing it away makes the infection harder to diagnose.
Urinating after sex is fine and may help reduce the risk of urinary tract infections, but it won’t prevent pregnancy or STIs. Gentle external washing with water is all the hygiene you need.
Pregnancy Tests and Timing
Home pregnancy tests work by detecting a hormone that rises after a fertilized egg implants in the uterus. This process takes roughly 6 to 12 days after conception, so testing before your missed period often yields unreliable results. For the most accurate answer, wait until the first day of your expected period or, ideally, one week after a missed period. If the result is negative but your period still hasn’t arrived, test again a few days later.