Identify your most fertile days and estimated delivery date.
Approximate Ovulation Date:
Most Fertile Window:
Next Period Due Date:
Due Date (If you conceive):
How Does the Ovulation Calculator Work?
Our free ovulation calculator helps you track your menstrual cycle to determine the specific days you are most likely to conceive. By entering the first day of your last menstrual period and the average length of your cycle, the tool uses the Standard Days Method to estimate your ovulation window.
Typically, ovulation occurs about 14 days before your next period starts. If you have a 28-day cycle, you likely ovulate on day 14. However, every woman's body is different. This tool calculates the "Fertile Window," which includes the five days leading up to ovulation and the day of ovulation itself. This is because sperm can live inside the female reproductive tract for up to five days, while an egg survives for about 12 to 24 hours after release.
Understanding Your Fertile Window
If you are trying to get pregnant, timing is everything. The fertile window is the six-day interval that concludes on the day of ovulation. Clinical studies suggest that the highest probability of conception occurs in the two days leading up to and including the day of ovulation.
Example Calculation
Suppose your last period began on October 1st and you have a regular 28-day cycle:
Next Period: October 29th
Ovulation Date: October 15th (14 days before the next period)
Fertile Window: October 10th to October 15th
Estimated Due Date: July 8th of the following year (if conception occurs)
Signs of Ovulation to Watch For
While a calculator provides a mathematical estimate, observing your body's physical signs can increase accuracy:
Basal Body Temperature (BBT) Changes: A slight rise in resting temperature after ovulation.
Cervical Mucus: Changes to a clear, slippery, "egg-white" consistency.
Ovulation Predictor Kits (OPKs): These tests detect a surge in Luteinizing Hormone (LH) in your urine.
Mild Pelvic Twinges: Some women feel a slight cramp or "mittelschmerz" when the egg is released.
function calculateOvulation() {
var lastPeriodInput = document.getElementById('lastPeriodDate').value;
var cycleLength = parseInt(document.getElementById('cycleLength').value);
if (!lastPeriodInput) {
alert("Please select the date of your last period.");
return;
}
if (isNaN(cycleLength) || cycleLength 45) {
alert("Please enter a valid cycle length (typically between 20 and 45 days).");
return;
}
var lastPeriodDate = new Date(lastPeriodInput);
// 1. Calculate Next Period
var nextPeriodDate = new Date(lastPeriodDate);
nextPeriodDate.setDate(lastPeriodDate.getDate() + cycleLength);
// 2. Calculate Ovulation Date (Standard: 14 days before next period)
var ovulationDate = new Date(nextPeriodDate);
ovulationDate.setDate(nextPeriodDate.getDate() – 14);
// 3. Calculate Fertile Window (5 days before ovulation + day of ovulation)
var fertileStart = new Date(ovulationDate);
fertileStart.setDate(ovulationDate.getDate() – 5);
var fertileEnd = new Date(ovulationDate);
// 4. Calculate Due Date (Naegele's Rule: Last period + 280 days)
var dueDate = new Date(lastPeriodDate);
dueDate.setDate(lastPeriodDate.getDate() + 280);
// Formatting Dates
var options = { month: 'long', day: 'numeric', year: 'numeric' };
document.getElementById('ovulationDateVal').innerText = ovulationDate.toLocaleDateString(undefined, options);
document.getElementById('fertileWindowVal').innerText = fertileStart.toLocaleDateString(undefined, options) + " – " + fertileEnd.toLocaleDateString(undefined, options);
document.getElementById('nextPeriodVal').innerText = nextPeriodDate.toLocaleDateString(undefined, options);
document.getElementById('dueDateVal').innerText = dueDate.toLocaleDateString(undefined, options);
// Show Result
document.getElementById('ovulationResult').style.display = 'block';
}