Menstrual Cycle Period Calculator

Menstrual Cycle & Period Predictor

(Typically 21-35 days)

(Typically 10-16 days, default 14)

Your Cycle Predictions:

Next Predicted Period Start:

Predicted Ovulation Date:

Predicted Fertile Window:

function calculateCycle() { var lastPeriodStartDateInput = document.getElementById("lastPeriodStartDate").value; var cycleLengthInput = document.getElementById("cycleLength").value; var lutealPhaseLengthInput = document.getElementById("lutealPhaseLength").value; if (!lastPeriodStartDateInput) { alert("Please enter your Last Period Start Date."); return; } var lastPeriodStart = new Date(lastPeriodStartDateInput); lastPeriodStart.setHours(0, 0, 0, 0); // Normalize to start of day var cycleLength = parseInt(cycleLengthInput); if (isNaN(cycleLength) || cycleLength 45) { alert("Please enter a valid Average Cycle Length (21-45 days)."); return; } var lutealPhaseLength = parseInt(lutealPhaseLengthInput); if (isNaN(lutealPhaseLength) || lutealPhaseLength 16) { lutealPhaseLength = 14; // Default to 14 if invalid or out of typical range document.getElementById("lutealPhaseLength").value = 14; // Update input field } // Calculate Next Predicted Period Start Date var nextPeriodDate = new Date(lastPeriodStart); nextPeriodDate.setDate(lastPeriodStart.getDate() + cycleLength); // Calculate Ovulation Date // Ovulation typically occurs lutealPhaseLength days BEFORE the next period var ovulationDate = new Date(nextPeriodDate); ovulationDate.setDate(nextPeriodDate.getDate() – lutealPhaseLength); // Calculate Fertile Window (typically 5 days before ovulation to 1 day after ovulation) var fertileWindowStart = new Date(ovulationDate); fertileWindowStart.setDate(ovulationDate.getDate() – 5); var fertileWindowEnd = new Date(ovulationDate); fertileWindowEnd.setDate(ovulationDate.getDate() + 1); // Format dates for display var options = { year: 'numeric', month: 'long', day: 'numeric' }; document.getElementById("nextPeriodDate").innerText = nextPeriodDate.toLocaleDateString('en-US', options); document.getElementById("ovulationDate").innerText = ovulationDate.toLocaleDateString('en-US', options); document.getElementById("fertileWindow").innerText = fertileWindowStart.toLocaleDateString('en-US', options) + " – " + fertileWindowEnd.toLocaleDateString('en-US', options); document.getElementById("cycleResult").style.display = "block"; }

Understanding Your Menstrual Cycle

The menstrual cycle is a complex series of hormonal and physiological changes that prepare a woman's body for a potential pregnancy each month. Understanding your cycle can be incredibly empowering, whether you're trying to conceive, avoid pregnancy, or simply monitor your reproductive health.

What is a Menstrual Cycle?

A menstrual cycle is counted from the first day of one period to the first day of the next. The average cycle length is 28 days, but it can vary significantly from person to person, typically ranging from 21 to 35 days. The cycle is divided into four main phases:

1. Menstrual Phase: This is when you have your period, typically lasting 3-7 days. It starts on Day 1 of your cycle.
2. Follicular Phase: This phase begins on the first day of your period and lasts until ovulation. During this time, follicles in your ovaries mature, preparing an egg for release.
3. Ovulation Phase: Around the middle of your cycle, a mature egg is released from the ovary. This is the most fertile time.
4. Luteal Phase: After ovulation, the ruptured follicle transforms into the corpus luteum, which produces progesterone to prepare the uterus for pregnancy. If pregnancy doesn't occur, the corpus luteum breaks down, leading to a drop in hormones and the start of your next period. The luteal phase length is usually quite consistent for an individual, typically 10-16 days.

How Our Calculator Works

Our Menstrual Cycle & Period Predictor uses a simple, widely accepted method to estimate your future cycle dates. By inputting three key pieces of information, it can provide predictions for your next period, ovulation, and fertile window:

• Last Period Start Date: This is the foundation of the calculation. All predictions are based on this starting point.
• Average Cycle Length: This is the number of days from the start of one period to the start of the next. The more accurate your average, the more accurate your predictions will be.
• Luteal Phase Length: This is the number of days between ovulation and the start of your next period. While it can vary, 14 days is a common average. If you don't know yours, 14 days is a good default.

Understanding Your Results

• Next Predicted Period Start: This is the estimated date your next menstrual bleeding will begin.
• Predicted Ovulation Date: This is the estimated day your ovary will release an egg. This is a key date if you are trying to conceive.
• Predicted Fertile Window: This is the range of days when you are most likely to get pregnant. Sperm can live in the reproductive tract for up to 5 days, and an egg is viable for about 12-24 hours after ovulation. Therefore, the fertile window typically includes the 5 days leading up to ovulation, the day of ovulation, and the day after.

Important Considerations

While this calculator provides helpful estimates, it's crucial to remember that it's a predictive tool, not a diagnostic one. Several factors can influence your cycle length and ovulation timing, including:

• Stress
• Diet and exercise changes
• Illness
• Travel
• Medications
• Hormonal imbalances (e.g., PCOS)
• Breastfeeding
• Perimenopause

For the most accurate tracking, consider combining this calculator with other methods like basal body temperature (BBT) charting or ovulation predictor kits (OPKs). If you have irregular cycles or concerns about your reproductive health, please consult with a healthcare professional.