Identify your 2 most fertile days to increase your chances of conception.
Typical range: 21 to 42 days
Your Personalized Results
Predicted Ovulation–
Start Testing On–
Your Fertile Window:
–
These are the days when intercourse is most likely to lead to pregnancy. For best results, use your Clearblue Easy test daily starting from the "Start Testing" date.
Understanding Your Clearblue Ovulation Results
The Clearblue Easy Ovulation Calculator uses the Calendar Method combined with your average cycle length to estimate when your Luteinizing Hormone (LH) surge will occur. By identifying your peak fertility days, you can time intercourse more effectively.
How to Use Your Results
Your "Start Testing" date is specifically calculated to ensure you don't miss your LH surge. If you use Clearblue Digital Ovulation Tests, you are looking for a "Smiley Face" symbol which indicates your 2 most fertile days.
The Fertile Window: Sperm can live inside the female body for up to 5 days, but an egg survives for only 12-24 hours after release.
LMP: This is the very first day of bleeding, not the day your period ends.
Cycle Length: This is the total number of days from the first day of one period to the day before the next period starts.
Clearblue Advanced Digital vs. Easy Digital
While the standard Clearblue Easy Ovulation test tracks one hormone (LH), the Advanced Digital version tracks two (Estrogen and LH). This calculator provides a baseline for both, but the Advanced version typically identifies 4 or more fertile days, giving you even more opportunities to conceive.
function calculateFertility() {
var lmpInput = document.getElementById('lastPeriodDate').value;
var cycleInput = document.getElementById('cycleLength').value;
if (!lmpInput || !cycleInput) {
alert("Please enter both your last period date and cycle length.");
return;
}
var cycleLength = parseInt(cycleInput);
if (cycleLength 45) {
alert("Please enter a cycle length between 20 and 45 days.");
return;
}
var lmpDate = new Date(lmpInput);
// Logic: Ovulation occurs roughly 14 days before the next period
// Next Period = LMP + Cycle Length
// Ovulation = LMP + Cycle Length – 14
var ovulationDate = new Date(lmpDate);
ovulationDate.setDate(lmpDate.getDate() + (cycleLength – 14));
// Fertile Window starts 5 days before ovulation and ends 1 day after
var fertileStart = new Date(ovulationDate);
fertileStart.setDate(ovulationDate.getDate() – 5);
var fertileEnd = new Date(ovulationDate);
fertileEnd.setDate(ovulationDate.getDate() + 1);
// Clearblue Testing Start: Usually 17 days before the next period (for a 28 day cycle)
// Formula: (Cycle Length – 17) days after LMP
var testingStart = new Date(lmpDate);
testingStart.setDate(lmpDate.getDate() + (cycleLength – 17));
// Formatting dates
var options = { month: 'short', day: 'numeric', year: 'numeric' };
document.getElementById('ovulationDay').innerText = ovulationDate.toLocaleDateString('en-US', options);
document.getElementById('startTesting').innerText = testingStart.toLocaleDateString('en-US', options);
document.getElementById('fertileWindow').innerText = fertileStart.toLocaleDateString('en-US', options) + " – " + fertileEnd.toLocaleDateString('en-US', options);
document.getElementById('fertilityResults').style.display = 'block';
// Smooth scroll to results
document.getElementById('fertilityResults').scrollIntoView({ behavior: 'smooth', block: 'nearest' });
}
#clearblue-calculator-wrapper input:focus {
outline: none;
border-color: #003a70 !important;
box-shadow: 0 0 0 3px rgba(0, 58, 112, 0.1);
}
#clearblue-calculator-wrapper button:hover {
background-color: #c21566 !important;
}
@media (max-width: 600px) {
#clearblue-calculator-wrapper div[style*="grid-template-columns: 1fr 1fr"] {
grid-template-columns: 1fr !important;
}
}