Period & Ovulation Calculator
Predict your next period, ovulation day, and fertile window based on your cycle history. Free, private, no sign-up.
📅 Enter Your Cycle Details
📊 Your Results
📋 Upcoming Period Forecast
ℹ️ How the Calculator Works
Our period calculator uses your last menstrual period (LMP) date and average cycle length to forecast upcoming cycles, based on established gynecological models.
Enter Last Period Date
Input Day 1 of your most recent period — the first day of bleeding.
Select Cycle Length
Count days from the start of one period to the start of the next. Most women: 21–35 days.
Get Instant Predictions
See your next period date, ovulation day, fertile window, and a multi-month forecast.
Plan Ahead
Use results to plan events, track symptoms, or understand your fertile days.
🔄 The 4 Phases of Your Cycle
The menstrual cycle has four distinct phases, each driven by hormonal changes that prepare the body for potential pregnancy. Understanding these phases helps you recognise normal patterns and fertility signals.
Days 1–5
Menstrual Phase
The uterine lining sheds, causing your period. Estrogen and progesterone are at their lowest. Typically lasts 3–7 days.
Days 1–13
Follicular Phase
Estrogen rises, the uterine lining rebuilds, and follicles develop in the ovary. Energy levels typically increase.
~Day 14
Ovulation Phase
A surge in LH hormone triggers egg release. This is the most fertile point — typically 14 days before your next period.
Days 15–28
Luteal Phase
Progesterone rises to prepare for potential pregnancy. If fertilisation doesn't occur, hormone levels drop, triggering the next period.
📖 About This Calculator
How Does a Period Calculator Work?
A period calculator uses your last period start date and average cycle length to predict future periods. Most cycles range from 21–35 days, with 28 days being average. Ovulation typically occurs 14 days before your next period.
Understanding Your Fertile Window
The fertile window spans roughly 6 days — the 5 days before ovulation plus ovulation day itself. Sperm can survive up to 5 days inside the body, so tracking this window is key for both conception planning and cycle awareness.
How Accurate Is a Period Calculator?
Period calculators are most accurate when your cycles are regular. For irregular cycles, results may vary by a few days. Stress, illness, travel, and hormonal changes can all affect cycle timing. For best accuracy, log several cycles over 3–6 months.
What Is a Normal Cycle Length?
A normal menstrual cycle ranges from 21 to 35 days, with 28 days being the commonly cited average. Research shows the actual average is closer to 29–30 days. A cycle is considered regular if it consistently falls within the 21–35 day range.