Period Calculator

Track your menstrual cycle and predict your next period dates, ovulation, and fertile window. Get comprehensive cycle analysis and personalized predictions.

Cycle Information

First day of your last menstrual period

days

Range: 21-35 days (average: 28 days)

days

Range: 2-7 days (average: 5 days)

Enter your cycle information to see predictions for your next periods, ovulation dates, fertile windows, and comprehensive cycle analysis.

Complete User Guide

What is the Menstrual Cycle?

The menstrual cycle is a natural process that occurs in the female reproductive system, typically lasting 21-35 days (average 28 days). It involves hormonal changes that prepare the body for potential pregnancy each month.

The cycle begins on the first day of menstruation (period) and ends the day before the next period starts. Understanding your cycle helps with fertility planning, health monitoring, and predicting period dates.

Menstrual Cycle Phases

Menstruation (Days 1-5)

The uterine lining is shed. This marks day 1 of your cycle. Typically lasts 3-7 days.

Follicular Phase (Days 1-13)

Follicles in the ovaries begin to mature. Estrogen levels rise, preparing the uterine lining for potential pregnancy.

Ovulation (Day 14, approximately)

A mature egg is released from the ovary. This is your most fertile day. The egg survives for 12-24 hours after release.

Fertile Window (5 days before + ovulation + 1 day after)

The best time for conception. Sperm can survive up to 5 days in the female reproductive tract, so having intercourse in the days leading up to ovulation increases chances of conception.

Luteal Phase (Days 15-28)

After ovulation, the corpus luteum produces progesterone. If pregnancy doesn't occur, hormone levels drop and menstruation begins.

How to Use This Calculator

  1. Enter the first day of your last menstrual period (the day bleeding started)
  2. Enter your average cycle length (number of days from day 1 of one period to day 1 of the next)
  3. Enter your average period length (how many days your period typically lasts)
  4. Click 'Calculate' to see predictions for your next periods, ovulation dates, and fertile windows
  5. Review the cycle calendar and phase distribution charts
  6. Use the predictions to plan ahead and track your cycle

Understanding Your Results

Next Period

Predicted start and end dates for your next menstrual period based on your cycle length and last period date.

Ovulation Date

Estimated date when ovulation occurs (typically 14 days before your next period). This is your most fertile day.

Fertile Window

The 6-7 day period when conception is most likely. This includes 5 days before ovulation, the day of ovulation, and 1 day after.

Current Cycle Day

Shows which day of your current cycle you are on. Day 1 is the first day of your last period.

Cycle Tracking Tips

Consistent Tracking

Track your period start dates for at least 3-6 months to get an accurate average cycle length. Mark dates on a calendar or use a period tracking app.

Note Symptoms

Track symptoms like cramps, mood changes, and flow intensity. This helps identify patterns and can be useful for healthcare consultations.

Irregular Cycles

If your cycles are very irregular (varying by more than 7 days), consider consulting with a healthcare provider. Irregular cycles can indicate underlying health conditions.

Important Notes

  • Period calculators provide estimates based on average cycle patterns. Actual timing can vary due to stress, illness, travel, hormonal changes, or medical conditions.
  • For more accurate tracking, combine calendar method with other methods like basal body temperature (BBT) charting, cervical mucus monitoring, or ovulation predictor kits.
  • If you have irregular cycles, PCOS, endometriosis, or other reproductive health concerns, consult with a healthcare provider or gynecologist for personalized guidance.
  • This calculator is for informational purposes only and should not replace professional medical advice. Always consult healthcare providers for reproductive health concerns, fertility planning, or if you experience unusual symptoms.

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