Estimate your cumulative probability of conception based on age and timeframe.
No known fertility issues
Minor irregularity (e.g., slightly irregular periods)
Known fertility factor (e.g., mild PCOS, endometriosis)
Severe fertility factor
Estimation Results
Estimated Chance Per Cycle (Fecundability):—
Cumulative Probability after N months:—
Likelihood Interpretation:—
Note: This tool uses general statistical data based on age and fecundability curves. It is for educational purposes only and cannot replace a medical diagnosis or fertility evaluation by a specialist.
How to Calculate Pregnancy Rate and Probability
Understanding the statistics behind conception can be empowering for couples trying to conceive. While "pregnancy rate" can refer to several metrics in medical literature (such as the Pearl Index for contraception or IVF success rates), in the context of natural conception, it typically refers to Fecundability and Cumulative Pregnancy Rate.
1. Fecundability: The Per-Cycle Probability
Fecundability is the probability of achieving a pregnancy within a single menstrual cycle. This number is heavily influenced by the age of the female partner. Biologically, fertility peaks in the early 20s and gradually declines, with a sharper decline after age 35.
General Fecundability Estimates by Age:
Age 20-24: ~25% chance per cycle
Age 25-29: ~20-25% chance per cycle
Age 30-34: ~15-20% chance per cycle
Age 35-39: ~10-15% chance per cycle
Age 40+: ~5% or less per cycle
2. The Cumulative Pregnancy Rate Formula
Most couples do not conceive in the very first month. The "Cumulative Pregnancy Rate" calculates the odds of getting pregnant over a period of time (several months). The mathematical formula used to calculate this is derived from the probability of not getting pregnant.
The Formula:
P = 1 – (1 – p)n
Where:
P = Cumulative probability of pregnancy.
p = Per-cycle probability (Fecundability).
n = Number of cycles/months trying.
Example Calculation
Let's calculate the pregnancy rate for a 30-year-old woman (assuming a 20% or 0.20 chance per cycle) trying for 6 months.
Calculate the chance of NOT getting pregnant in one month: 1 – 0.20 = 0.80.
Raise this to the power of the number of months (6): 0.806 ≈ 0.262. (This is the chance of not getting pregnant for 6 months straight).
Subtract from 1 to find the chance of success: 1 – 0.262 = 0.738.
Result: There is roughly a 73.8% chance of conceiving within those 6 months.
Medical Definitions of Pregnancy Rate
In clinical settings, pregnancy rates may also be calculated using the Pearl Index, primarily used to measure the efficacy of birth control methods. The Pearl Index represents the number of pregnancies per 100 woman-years of use.
However, for fertility purposes, the "Time to Pregnancy" (TTP) metric is more relevant. Statistics show that approximately 84% of couples will conceive within one year of regular unprotected intercourse if there are no underlying fertility issues.
function calculatePregnancyProbability() {
// 1. Get input values
var ageInput = document.getElementById('womanAge').value;
var monthsInput = document.getElementById('monthsTrying').value;
var healthFactor = document.getElementById('fertilityStatus').value;
// 2. Validate inputs
if (ageInput === "" || monthsInput === "") {
alert("Please enter both Age and Timeframe to calculate.");
return;
}
var age = parseFloat(ageInput);
var months = parseFloat(monthsInput);
var factor = parseFloat(healthFactor);
if (age 70) {
alert("Please enter a realistic age.");
return;
}
if (months < 0) {
alert("Months trying cannot be negative.");
return;
}
// 3. Determine Base Fecundability Rate based on Age
// These are statistical approximations for natural conception
var baseRate = 0.05; // Default low
if (age = 25 && age = 30 && age = 35 && age = 38 && age = 40 && age = 42) {
baseRate = 0.03; // drastically reduces
}
// 4. Apply Health Factor
var adjustedCycleRate = baseRate * factor;
// Cap rate to realistic max (it's rarely above 30% naturally per cycle even in perfect conditions)
if (adjustedCycleRate > 0.30) adjustedCycleRate = 0.30;
// 5. Calculate Cumulative Probability: P = 1 – (1 – p)^n
var probabilityOfFailure = 1 – adjustedCycleRate;
var cumulativeProbability = 1 – Math.pow(probabilityOfFailure, months);
// 6. Format Results
var perCyclePercent = (adjustedCycleRate * 100).toFixed(1) + "%";
var cumulativePercent = (cumulativeProbability * 100).toFixed(1) + "%";
// 7. Interpret Result
var interpretation = "";
if (cumulativeProbability < 0.2) {
interpretation = "Low probability within this timeframe.";
} else if (cumulativeProbability < 0.5) {
interpretation = "Moderate probability.";
} else if (cumulativeProbability < 0.8) {
interpretation = "High probability.";
} else {
interpretation = "Very high probability.";
}
// 8. Update DOM
document.getElementById('perCycleResult').innerHTML = perCyclePercent;
document.getElementById('cumulativeResult').innerHTML = cumulativePercent;
document.getElementById('monthsDisplay').innerHTML = months;
document.getElementById('interpretationResult').innerHTML = interpretation;
// Show results container
document.getElementById('resultsArea').style.display = "block";
}