🔗 Use full-page Period Calculator here for best experience
How to Use the Period Calculator
- Enter the first day of your last period — this is Day 1 of your cycle
- Enter your average cycle length — most women have a 21–35 day cycle (average: 28)
- Enter your period duration — how many days your period typically lasts
- Click Calculate — instantly see your next period, ovulation date, fertile window, and 6-cycle forecast
Understanding Your Menstrual Cycle
A menstrual cycle is counted from Day 1 of your period to Day 1 of the next period. The average is 28 days, but anything between 21 and 35 days is considered normal.
The 4 Phases of the Cycle
| Phase | Days (28-day cycle) | What’s Happening |
|---|---|---|
| Menstruation | Days 1–5 | Uterine lining sheds |
| Follicular Phase | Days 1–13 | Follicles mature, oestrogen rises |
| Ovulation | Day 14 | Egg released — peak fertility |
| Luteal Phase | Days 15–28 | Progesterone rises; body prepares for pregnancy |
When Do You Ovulate?
Ovulation typically occurs 14 days before the start of your next period — not necessarily on Day 14 of your cycle. For a 28-day cycle, that’s Day 14. For a 32-day cycle, it’s Day 18.
The Fertile Window
You can only get pregnant during a small window around ovulation:
- Sperm can survive 3–5 days inside the reproductive tract
- An egg survives 12–24 hours after ovulation
- Your fertile window is approximately 6 days: the 5 days before ovulation + ovulation day itself
What Affects Cycle Regularity?
- Stress and major life changes
- Significant weight changes
- Intense exercise
- Hormonal contraceptive changes
- Thyroid conditions
- Polycystic ovary syndrome (PCOS)
- Perimenopause
Signs of Ovulation to Look For
- Cervical mucus changes — egg-white consistency around ovulation
- Mild pelvic pain (mittelschmerz) on one side
- Basal body temperature rises slightly (0.2–0.5°C) after ovulation
- Libido increase — nature’s nudge
- Light spotting in some women
Period Calculator vs Period Tracking Apps
Our calculator is fast and private — no account required, no data stored. For long-term tracking and pattern recognition, dedicated apps like Clue or Flo can identify trends across many cycles. This calculator is best for quick predictions and cycle planning.
Important Disclaimer
This calculator provides estimates only based on average cycle patterns. Cycle length varies naturally from month to month. This tool is not a method of contraception and should not be used to prevent or plan pregnancy without medical guidance. Consult a healthcare provider for personalised fertility advice.
Predict My Next PeriodRelated Tools:
- Due Date Calculator — calculate your pregnancy due date
- Age Calculator — calculate exact age in days, months, years
- Date Duration Calculator — calculate time between any two dates