Monthly Period Cycle Calculator

Monthly Period & Ovulation Calculator

Usually 21-35 days

Your Cycle Predictions:

Next Period Starts:

Estimated Ovulation Day:

Peak Fertile Window:

Next Expected Due Date (if conceived):

function calculateCycle() { var lastDateVal = document.getElementById("lastPeriodDate").value; var cycleLength = parseInt(document.getElementById("cycleLength").value); var periodDuration = parseInt(document.getElementById("periodDuration").value); if (!lastDateVal || isNaN(cycleLength)) { alert("Please select the date of your last period."); return; } var lastDate = new Date(lastDateVal); // Calculate Next Period var nextPeriod = new Date(lastDate); nextPeriod.setDate(lastDate.getDate() + cycleLength); // Calculate Ovulation (typically 14 days before next period) var ovulationDate = new Date(nextPeriod); ovulationDate.setDate(nextPeriod.getDate() – 14); // Fertile Window (5 days before ovulation + ovulation day) var fertileStart = new Date(ovulationDate); fertileStart.setDate(ovulationDate.getDate() – 5); // Estimated Due Date (Naegele's Rule: LMP + 280 days) var dueDate = new Date(lastDate); dueDate.setDate(lastDate.getDate() + 280); var options = { weekday: 'long', year: 'numeric', month: 'long', day: 'numeric' }; document.getElementById("nextPeriodDisplay").innerText = nextPeriod.toLocaleDateString(undefined, options); document.getElementById("ovulationDisplay").innerText = ovulationDate.toLocaleDateString(undefined, options); document.getElementById("fertileDisplay").innerText = fertileStart.toLocaleDateString(undefined, { month: 'short', day: 'numeric' }) + " to " + ovulationDate.toLocaleDateString(undefined, { month: 'short', day: 'numeric' }); document.getElementById("dueDateDisplay").innerText = dueDate.toLocaleDateString(undefined, options); document.getElementById("periodResults").style.display = "block"; }

Understanding Your Monthly Period Cycle

A monthly period cycle calculator is an essential tool for tracking reproductive health, identifying fertile windows, and planning for upcoming menstrual cycles. Most people assume a cycle is exactly 28 days, but in reality, a healthy cycle can range anywhere from 21 to 35 days.

How to Calculate Your Cycle Length

Your cycle length is the number of days between the first day of one period and the first day of the next. To get the most accurate result from this calculator, you should track your cycle for at least three months and use the average number of days.

• The Follicular Phase: This starts on the first day of your period and ends at ovulation.
• Ovulation: This is when an egg is released from the ovary. It usually happens 14 days before your next period begins.
• The Luteal Phase: The time between ovulation and your next period. This is typically the most consistent part of the cycle.

Identifying Your Fertile Window

If you are trying to conceive, timing is critical. Sperm can live inside the female reproductive tract for up to 5 days, while an egg survives for only 12-24 hours after release. Therefore, your "fertile window" includes the five days leading up to ovulation and the day of ovulation itself.

Example Calculation

If your last period started on January 1st and you have a 28-day cycle:

• Next Period: January 29th
• Ovulation Day: January 15th
• Fertile Window: January 10th – January 15th

When to See a Doctor

While minor fluctuations are normal, you should consult a healthcare provider if:

• Your cycles are consistently shorter than 21 days or longer than 35 days.
• Your period lasts longer than 7 days.
• You experience severe pain that interferes with daily activities.
• Your periods stop for more than three months (and you are not pregnant).

Disclaimer: This calculator provides estimates for informational purposes only. It should not be used for contraception or as a definitive medical diagnosis.