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 (plus optional age/BMI) and any emergency contraception to give a clear percent risk, 1-in-N view, and your first accurate test day

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.

If the encounter occurred well outside of this fertile window (for example, during your period or just before it was due to start), the chance of pregnancy is extremely low. Our calculator uses your dates to pinpoint where you likely were in this cycle.

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: For the most accurate result, you should wait until at least 14 days after your estimated ovulation date, or the first day of your missed period. Testing earlier can result in a false negative, even if you have successfully conceived.

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 weighting based on where the intercourse falls within your specific fertile window.
• Mitigation: Risk reduction calculated based on the type and timing of any emergency contraception (EC) used.

1. Cycle-Day Weighting

We model a standard 6-day fertile window (the five days preceding ovulation plus the day of ovulation itself). Risk is highest on the day before and the day of ovulation. This aligns with prospective data showing that conception risk is almost entirely concentrated within this interval.Source: Wilcox et al., NEJM 1995.

The model also accounts for sperm survival, assuming sperm can remain viable in fertile cervical mucus for up to 5 days.Source: MSD Manual (Global).

2. From Baseline to Day-Specific Risk

We estimate the ovulation date using the standard calculation (Ovulation ≈ Cycle Length minus 14 days). A normalized curve scales the baseline probability according to the specific cycle day entered. Days outside the fertile window are assigned extremely low probabilities, while peak fertile days receive the highest weights. Results smaller than a specific threshold are displayed as "<0.0001%" rather than 0% to reflect that biological anomalies can occur.

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. Recommended Testing Window

To avoid false negatives, we calculate the "First Accurate Test Date" based on the day your next period is due (approximately 14 days post-ovulation). If cycle timing is irregular or unknown, the standard medical recommendation is to test 21 days after the unprotected intercourse.Source: Mayo Clinic: Home Pregnancy Tests.

Important Safeguards

• Maximum Efficacy: If you are within 5 days of intercourse, the Copper IUD is the most effective method available (CDC).
• 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.