Calculate Pregnancy Chance After Intercourse Without Contraception

Find your estimated pregnancy chance after one encounter where no contraception was used. This tool weighs cycle day, optional age/BMI, and emergency contraception timing to estimate percent risk, a 1-in-N view, and a pregnancy-test date.

* Calendar dates cannot confirm ovulation or identify a safe day. This is an approximate per-act estimate, not a measured personal chance. The test date is 21 days after this encounter; you can also test from the first day of a missed period. Count from the latest potentially unprotected encounter if you have sex again.

Understanding Your Pregnancy Risk: It's All About Timing

Your chance of conceiving is not the same every day of the month. It is concentrated within a specific period known as the fertile window.

• What is the Fertile Window? This is a roughly six-day period that includes the five days leading up to ovulation and the day of ovulation itself. This is the only time during your cycle when pregnancy is possible.
• What is Ovulation? Ovulation is when one of your ovaries releases an egg. The egg can only survive for about 12-24 hours, but sperm can live inside the female reproductive tract for up to five days. This is why the fertile window begins before you actually ovulate.
• Peak Fertility: Your chances are highest in the 2-3 days immediately preceding and including ovulation. Intercourse on these days carries the highest probability of pregnancy, often estimated to be between 20-45% for young, healthy couples, depending on various health factors.

Ovulation can happen earlier or later than expected, even with regular cycles. Your period dates provide an estimate of timing; they cannot confirm that an encounter was outside your fertile window.

What Are the Next Steps?

After getting your estimate, it's important to know what to do next.

If You Are Trying to Avoid Pregnancy:

If you are concerned about an unplanned pregnancy, time is critical.

• Emergency Contraception (EC): Options such as emergency contraception pills work best when used as soon as possible after intercourse where no contraception was used. A copper IUD is another highly effective form of emergency contraception.
• Consult a Professional: Please speak with a pharmacist or healthcare provider immediately to discuss your best options. They can provide confidential advice tailored to your situation.

Used the withdrawal method for that encounter? Get a more specific estimate with the withdrawal method risk calculator.

If You Are Trying to Conceive:

If the encounter was intentional, the next key date is when you can take a reliable pregnancy test.

• When to Test: Test from the first day of a missed period, or at least 21 days after the last unprotected sex if you do not know when your next period is due. Testing too early can give a false negative.

Disclaimer: This calculator provides a statistical estimate and is for informational purposes only. It is not a substitute for a medical diagnosis or professional advice. Always consult with a healthcare provider for any health concerns.

Methodology

What This Tool Estimates

This calculator provides an educational estimate of pregnancy probability following a single act of unprotected vaginal intercourse. It is not a medical diagnosis. The calculation synthesizes three key factors:

• Baseline Risk: A per-act probability derived from our internal risk engine (accounting for age, BMI, and context).
• Cycle Timing: A population-based calendar-day pattern allowing for variation in ovulation timing.
• Mitigation: Risk reduction calculated based on the type and timing of any emergency contraception (EC) used.

1. Calendar-day timing

Cycle day 1 is the first day of your period. Calendar timing follows the all-women estimates for days 1-40 in Li, Wilcox and Dunson (2015), Table 3. These estimates allow for variation in ovulation timing rather than treating a predicted ovulation date as certain.

The selected day's reference value is divided by the mean reference over your entered cycle length, limited to the 40 published days. This relative factor scales the average per-act estimate; it does not move the peak to a fixed number of days before your next period. This scaling is a modeling approximation, not a measured individual probability. Dates before the entered period or after day 40 use an average estimate without a cycle-day adjustment. Passing your usual cycle length does not confirm that a new period began.

2. Interpreting the estimate

The percentage combines that timing pattern with the age and lifestyle model. Results remain approximate. No calendar date establishes a safe day, and the calculation does not confirm ovulation. Results are capped at 40%; extremely small values are shown as below the display threshold.

3. Emergency Contraception (EC) Adjustments

We apply specific risk-reduction factors based on the method used and the time elapsed since intercourse:

• Levonorgestrel (e.g., Plan B): Most effective when taken within 72 hours (3 days). Efficacy declines over time and may be lower in individuals with a higher BMI. We apply a reduction factor that adjusts for both timing and BMI.Sources: ACOG Practice Bulletin; WHO Fact Sheet.
• Ulipristal Acetate (e.g., ella): Effective for up to 120 hours (5 days). Clinical trials indicate it is more effective than Levonorgestrel, particularly in the 72–120 hour window or closer to ovulation. We model a sustained efficacy across the 5-day window.Sources: Glasier et al., The Lancet 2010; Planned Parenthood Guidelines.
• Copper IUD: The most effective form of EC. If inserted within 5 days of intercourse (or 5 days after estimated ovulation), the failure rate is less than 0.1%. We model this as a ~99% risk reduction.Sources: CDC: Emergency Contraception; ACOG FAQs.

4. Pregnancy testing

The displayed date is 21 calendar days after intercourse. You can test from the first day of a missed period, or at least 21 days after the last unprotected sex if the next period date is unclear. A negative test taken too early may need repeating. NHS: Doing a pregnancy test.

Important Safeguards

• Maximum Efficacy: If you are within 5 days of intercourse, the Copper IUD is the most effective method available (CDC Emergency Contraception).
• Timing Matters: Oral pills differ in longevity; Ulipristal acetate (UPA) generally outperforms Levonorgestrel (LNG) in the 72–120 hour window.
• Urgent Symptoms: Seek immediate medical attention if you experience severe abdominal pain, dizziness, or heavy bleeding, as these may indicate complications distinct from typical pregnancy risk.