Estimate your most fertile days and next cycle dates.
Estimated Ovulation Date:
Next Period Starts:
Pregnancy Test Date:
Your Fertile Window:
How to Calculate Your Ovulation Cycle
Understanding your ovulation cycle is the foundation of reproductive health, whether you are trying to conceive or simply tracking your biological rhythms. Ovulation is the process where a mature egg is released from the ovary, making it available for fertilization.
The Math Behind the Window
A standard menstrual cycle is measured from the first day of one period to the first day of the next. While 28 days is the "average," cycles typically range from 21 to 35 days. The logic used in this calculator follows the Luteal Phase principle: ovulation usually occurs approximately 14 days before your next period begins.
The Fertile Window: This includes the day of ovulation and the five days preceding it. Sperm can survive inside the female reproductive tract for up to 5 days, while an egg is only viable for 12 to 24 hours after release.
The Peak Day: This is the day of ovulation and the day prior, representing your highest chance of conception.
Example Calculation
If your last period started on January 1st and you have a 30-day cycle:
Your next period is expected on January 31st.
Counting back 14 days, your ovulation date is January 17th.
Your fertile window would be January 12th through January 17th.
Signs of Ovulation to Watch For
While a calculator provides a mathematical estimate, your body often provides physical cues:
Basal Body Temperature: A slight rise in resting temperature after ovulation.
Cervical Mucus: A change in consistency to something resembling "egg whites" indicates high fertility.
Ovulation Predictor Kits (OPKs): These tests detect a surge in Luteinizing Hormone (LH) in your urine.
function calculateOvulation() {
var lastPeriodInput = document.getElementById('last_period').value;
var cycleLength = parseInt(document.getElementById('cycle_length').value);
if (!lastPeriodInput || isNaN(cycleLength)) {
alert("Please enter a valid date and cycle length.");
return;
}
var lastDate = new Date(lastPeriodInput);
// Create new dates to avoid mutating the original
var nextPeriod = new Date(lastDate);
nextPeriod.setDate(lastDate.getDate() + cycleLength);
var ovulationDate = new Date(nextPeriod);
ovulationDate.setDate(nextPeriod.getDate() – 14);
var fertileStart = new Date(ovulationDate);
fertileStart.setDate(ovulationDate.getDate() – 5);
var testDate = new Date(nextPeriod);
testDate.setDate(nextPeriod.getDate() + 1);
// Format function
var options = { month: 'long', day: 'numeric', year: 'numeric' };
document.getElementById('ovulation_date').innerText = ovulationDate.toLocaleDateString(undefined, options);
document.getElementById('next_period').innerText = nextPeriod.toLocaleDateString(undefined, options);
document.getElementById('test_date').innerText = testDate.toLocaleDateString(undefined, options);
document.getElementById('fertile_window').innerText = fertileStart.toLocaleDateString(undefined, options) + " to " + ovulationDate.toLocaleDateString(undefined, options);
document.getElementById('ovulation-results').style.display = 'block';
}