Chances of Getting Pregnant After Sex/Data

This subpage contains the data and risk models used on the main page. The data is based on population averages and is used to generate a risk estimate.

Baseline Fertility Parameters

These are single-value constants used in the risk model calculation.

• Peak Conception Probability (A): 0.33
• Fertile Window Width (σ, in days): 2.5
• Approximation of 'e': 2.71828

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Age-Related Fertility

This table provides a final multiplier based on the woman's age, which adjusts the overall result from the bell curve calculation.

age_description	age_multiplier
Under 25	1.0
25-30	0.9
31-39	0.65
40 and over	0.25

• Reference: Age and Fertility: A Guide for Patients, American Society for Reproductive Medicine (ASRM), 2021.

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Menstrual Cycle Profile

This table provides the estimated peak ovulation day (μ) for different cycle profiles. A value of -1 indicates an irregular cycle where a peak cannot be reliably predicted.

cycle_description	cycle_ovulation_day_mu
Regular and short (25 days or less)	11
Regular and average (26-31 days)	14
Regular and long (32 days or more)	18
Irregular or I don't know	-1

• Reference: Your Menstrual Cycle, Office on Women's Health, U.S. Department of Health & Human Services, 2021.

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Timing of Intercourse

This table converts the user's time window into a single day of the cycle (x) for use in the calculation (using the midpoint of the range).

timing_description	timing_intercourse_day_x
1-7 days before (During or just after my period)	4
8-13 days before (About a week after my period)	11
14-20 days before (About two weeks after my period)	17
21-28 days before (In the week my next period was due)	25
More than 28 days before	-1

• Reference: Based on standard menstrual cycle phases.

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Risk Models

This model uses a Gaussian (bell curve) function to estimate risk, approximating the mathematical constant 'e' with 2.71828.

  RiskModel: Chances of Getting Pregnant After Sex/Data:PregnancyRiskPerEvent
    Content: 
'''Result:''' {{#ifexpr: {cycle_ovulation_day_mu} < 0 or {timing_intercourse_day_x} < 0
| ''Because your cycle is irregular or the timing is too uncertain, it's not possible to provide a reliable estimate with this tool.''
| Your estimated chance of pregnancy is about '''{{One_In_X|{result}}}''' from this event.
}}

{{#ifexpr: {result} > 0.01
|== What You Can Do Now ==
If you have had unprotected sex recently and do not wish to become pregnant, you have options. It's important to act quickly.

* '''Emergency Contraception (EC):''' Often called the "morning-after pill," EC can prevent pregnancy if taken soon after sex. It is most effective the sooner you take it, and can be used up to '''3-5 days''' after unprotected sex, depending on the type. You can often get EC from a pharmacy without a prescription.

* '''Talk to a Professional:''' A pharmacist, doctor, or a local health clinic (like a school nurse or Planned Parenthood) can provide confidential advice, EC, and other contraceptive options.
}}

Calculation Explanation: 🔢 This model calculates the distance in days between intercourse (`x`) and the estimated day of ovulation (`μ`), then inputs that distance into a bell curve formula to find the corresponding probability. This result is then adjusted by the age_multiplier. This method more accurately reflects the rise and fall of fertility throughout the cycle.

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Initially created by Gemini (Sept. 2025).