Estimate your conception date and pregnancy timeline based on your cycle.
Your Estimated Timeline
Estimated Conception Date:–
Conception Window:–
Estimated Due Date:–
Current Gestational Age:–
How to Use the Accurate Conception Calculator
This tool helps you backtrack or predict the moment of fertilization based on your Last Menstrual Period (LMP) and your average menstrual cycle length. While most calculators assume a standard 28-day cycle, this tool adjusts for your specific biology to provide more accurate results.
Understanding the Science
Conception typically occurs during ovulation, which happens roughly 14 days before your next period starts. If you have a 30-day cycle, you likely ovulated on day 16. If you have a 24-day cycle, ovulation likely occurred on day 10. By entering your cycle length, we can more accurately pinpoint the date the egg was released and fertilized.
Key Metrics Explained:
Conception Date: The most likely day fertilization occurred.
Conception Window: The 5-day period where intercourse most likely led to pregnancy, accounting for sperm longevity (up to 5 days) and egg viability (12-24 hours).
Due Date: Calculated using Naegele's Rule, adjusted for your cycle length.
Realistic Example:
If your Last Menstrual Period began on September 1st and you have a 30-day cycle:
Ovulation (Conception) would be around September 17th (16 days after LMP).
Your Conception Window would range from September 12th to September 18th.
Your Estimated Due Date would be June 10th of the following year.
Disclaimer: This calculator is for informational purposes only. Only a medical professional using ultrasound and clinical data can provide a definitive gestational age and due date.
function calculateConception() {
var lmpInput = document.getElementById('lmpDate').value;
var cycleLength = parseInt(document.getElementById('cycleLength').value);
if (!lmpInput) {
alert("Please select the first day of your last period.");
return;
}
if (isNaN(cycleLength) || cycleLength 45) {
alert("Please enter a valid cycle length between 20 and 45 days.");
return;
}
var lmpDate = new Date(lmpInput);
// 1. Calculate Conception Date
// Formula: LMP + (Cycle Length – 14 days)
var conceptionDate = new Date(lmpDate);
conceptionDate.setDate(lmpDate.getDate() + (cycleLength – 14));
// 2. Calculate Conception Window (3 days before to 1 day after)
var windowStart = new Date(conceptionDate);
windowStart.setDate(conceptionDate.getDate() – 3);
var windowEnd = new Date(conceptionDate);
windowEnd.setDate(conceptionDate.getDate() + 1);
// 3. Calculate Due Date (LMP + 280 days + adjustment for cycle)
// Standard is 280 days for 28 day cycle. Adjust based on cycle.
var cycleAdjustment = cycleLength – 28;
var dueDate = new Date(lmpDate);
dueDate.setDate(lmpDate.getDate() + 280 + cycleAdjustment);
// 4. Current Gestational Age
var today = new Date();
var diffTime = Math.abs(today – lmpDate);
var diffDays = Math.floor(diffTime / (1000 * 60 * 60 * 24));
var weeks = Math.floor(diffDays / 7);
var days = diffDays % 7;
// Formatting options
var options = { month: 'long', day: 'numeric', year: 'numeric' };
// Display results
document.getElementById('resConception').innerText = conceptionDate.toLocaleDateString(undefined, options);
document.getElementById('resWindow').innerText = windowStart.toLocaleDateString(undefined, { month: 'short', day: 'numeric' }) + " – " + windowEnd.toLocaleDateString(undefined, { month: 'short', day: 'numeric', year: 'numeric' });
document.getElementById('resDue').innerText = dueDate.toLocaleDateString(undefined, options);
if (today < lmpDate) {
document.getElementById('resAge').innerText = "Future Date Selected";
} else {
document.getElementById('resAge').innerText = weeks + " Weeks, " + days + " Days";
}
document.getElementById('conception-result').style.display = 'block';
}