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. The descriptions are linked to the primary sources.

• Peak Conception Probability (A): 0.33
• Fertile Window Width (σ, in days): 2.5

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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, 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
Don't know/unsure	-1
1-7 days (During or just after my period)	4
8-13 days (About a week after my period)	11
14-20 days (About two weeks after my period)	17
21-28 days (In the week my next period was due)	25
More than 28 days	-1

• Reference: Based on standard menstrual cycle phases.

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Contraception Use Case Logic

This table provides mutually exclusive multipliers to simulate conditional logic. Selecting a row sets one multiplier to 1 and the others to 0.

logic_description	logic_typical	logic_perfect	logic_failed
Unsure (Typical Use)	1	0	0
It was used correctly (Perfect Use)	0	1	0
It broke / there was a mistake (Failed Use)	0	0	1

Contraception Method

This table provides the failure rates for typical, perfect, and failed use cases for each method. A value of 1.0 means no risk reduction.

bc_description	bc_typical_mult	bc_perfect_mult	bc_failed_mult
None (unprotected sex)	1.0	1.0	1.0
Male Condom	0.13	0.02	1.0
The Pill (combined)	0.07	0.003	1.0
Withdrawal ("pulling out")	0.22	0.04	1.0
Hormonal IUD (Mirena, etc.)	0.002	0.002	1.0
Copper IUD (Paragard)	0.008	0.008	1.0
The Implant (Nexplanon)	0.001	0.001	1.0
The Shot (Depo-Provera)	0.04	0.006	1.0

• Reference: Contraception, U.S. Centers for Disease Control and Prevention (CDC).

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Risk Models

This model uses a Gaussian (bell curve) function to estimate risk.

  RiskModel: Chances of Getting Pregnant After Sex/Data:PregnancyRiskPerEvent
    Content: 
{{PregnancyResult
|{{#expr: 0.33*(e^(-0.5*(({timing_intercourse_day_x}-{cycle_ovulation_day_mu})/2.5)^2))*{age_multiplier}*( ({bc_typical_mult}*{logic_typical})+({bc_perfect_mult}*{logic_perfect})+({bc_failed_mult}*{logic_failed}) ) }}
|{{#expr: 0.33*{age_multiplier}*( ({bc_typical_mult}*{logic_typical})+({bc_perfect_mult}*{logic_perfect})+({bc_failed_mult}*{logic_failed}) ) }}
|{pagestate}
}}

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.

If the exact timing isn't known, the maximum fertility adjusted for age (0.33 * age_multiplier) times the birth control effectiveness factor will be shown instead.

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Initially created by Gemini (Sept. 2025).