Your next estimated period details will appear here.
Understanding Your Menstrual Cycle
The menstrual cycle is a natural monthly series of changes a woman's body goes through in preparation for the possibility of pregnancy. Each month, one of the ovaries releases an egg – a process called ovulation. At the same time, hormonal changes prepare the uterus for pregnancy. If ovulation takes place and the egg isn't fertilized by a sperm, the lining of the uterus sheds, causing menstrual bleeding, commonly known as a period.
How the Calculator Works
This calculator uses two key pieces of information you provide:
Date of Last Menstrual Period (LMP) Start: This is the first day you began bleeding from your last period.
Average Menstrual Cycle Length: This is the number of days from the start of one period to the start of the next. For most women, this is around 28 days, but it can vary significantly, typically ranging from 21 to 35 days.
Average Period Duration: This is the number of days you typically experience menstrual bleeding.
Calculating Your Next Period
The calculator performs the following steps:
Determine the start date of the next period: It adds your average menstrual cycle length to the start date of your last period.
Determine the end date of the next period: It adds your average period duration to the calculated start date of the next period.
Formula:
Next Period Start Date = LMP Start Date + (Cycle Length – 1) days
Next Period End Date = Next Period Start Date + (Period Duration – 1) days
Why Track Your Period?
Tracking your menstrual cycle can provide valuable insights into your reproductive health. It can help you:
Predict and prepare for your period each month.
Identify potential irregularities in your cycle that might warrant a discussion with a healthcare provider.
Understand your fertile window for family planning purposes.
Monitor symptoms related to your cycle, such as mood changes, pain, or acne.
Disclaimer: This calculator is an estimation tool and should not be used as a substitute for professional medical advice. Individual cycles can vary due to many factors including stress, illness, and hormonal changes. For accurate information about your reproductive health, please consult a healthcare professional.
function calculatePeriod() {
var lmpStartDateStr = document.getElementById("lastPeriodStart").value;
var cycleLength = parseInt(document.getElementById("cycleLength").value);
var periodDuration = parseInt(document.getElementById("periodDuration").value);
var resultDiv = document.getElementById("result");
resultDiv.innerHTML = ""; // Clear previous results
if (!lmpStartDateStr || isNaN(cycleLength) || isNaN(periodDuration) || cycleLength <= 0 || periodDuration <= 0) {
resultDiv.innerHTML = "Please enter valid dates and numbers for cycle length and duration.";
return;
}
var lmpStartDate = new Date(lmpStartDateStr);
// Calculate next period start date
// Add (cycleLength – 1) days because the cycle length *includes* the start day of the period
var nextPeriodStartDate = new Date(lmpStartDate);
nextPeriodStartDate.setDate(lmpStartDate.getDate() + cycleLength -1);
// Calculate next period end date
// Add (periodDuration – 1) days because the duration *includes* the start day of the period
var nextPeriodEndDate = new Date(nextPeriodStartDate);
nextPeriodEndDate.setDate(nextPeriodStartDate.getDate() + periodDuration – 1);
// Format dates for display
var options = { year: 'numeric', month: 'long', day: 'numeric' };
var formattedNextStartDate = nextPeriodStartDate.toLocaleDateString(undefined, options);
var formattedNextEndDate = nextPeriodEndDate.toLocaleDateString(undefined, options);
resultDiv.innerHTML =
"Estimated Next Period Start: " + formattedNextStartDate + "" +
"Estimated Next Period End: " + formattedNextEndDate + "";
}