ganak.appPeriod Calculator
Free period calculator. Predict your next period, safe days, fertile window, and ovulation. 6-month cycle calendar with predictions for 21–45 day cycles.
The date your most recent period started
Days between period starts. 28 is average.
How many days your period typically lasts. 5 days is the average.
Safe & Unsafe Period
Based on the calendar method (not a contraceptive replacement)
Safe Window (Early)
Apr 22 – Apr 24 (3 days)
Fertile / Unsafe Window
Apr 25 – Apr 30 · 6 unsafe days outside period
Safe Window (Late)
May 1 – May 14 (14 days)
The calendar method is not a reliable form of contraception. Cycles can vary, and this should only be used for general awareness. Consult a healthcare provider for birth control advice.
6-Month Period Calendar
Projected period dates, fertile windows, and ovulation
| # | Period | Fertile Window | Ovulation | Next Period |
|---|---|---|---|---|
| 1 | Apr 17 – Apr 21 | Apr 25 – Apr 30 | Apr 30 | May 15 |
| 2 | May 15 – May 19 | May 23 – May 28 | May 28 | Jun 12 |
| 3 | Jun 12 – Jun 16 | Jun 20 – Jun 25 | Jun 25 | Jul 10 |
| 4 | Jul 10 – Jul 14 | Jul 18 – Jul 23 | Jul 23 | Aug 7 |
| 5 | Aug 7 – Aug 11 | Aug 15 – Aug 20 | Aug 20 | Sep 4 |
| 6 | Sep 4 – Sep 8 | Sep 12 – Sep 17 | Sep 17 | Oct 2 |
Current cycle highlighted. Dates are estimates based on the calendar method and your average cycle length.
Add to Your Calendar
Sync your predicted period dates to your calendar
PMS Prediction
PMS symptoms typically start May 8 – May 15
Mood swings
Irritability, anxiety, or feeling emotional
Cramps & bloating
Lower abdominal pain and water retention
Breast tenderness
Soreness or swelling in the breasts
Fatigue
Feeling more tired than usual
Food cravings
Increased appetite or specific cravings
Headaches
Tension headaches or migraines
What Is a Period Calculator?
Predict your cycle dates using the calendar method
A period calculator predicts when your next menstrual period will start based on your last period date and average cycle length. It uses the calendar method to estimate upcoming periods, fertile windows, ovulation dates, and safe days over multiple cycles.
Period Dates
Predict start & end dates for upcoming periods
Safe & Unsafe Days
Identify low and high fertility windows
PMS Prediction
Know when premenstrual symptoms may start
How to Calculate Your Next Period Date
The formula behind your period predictions
Your next period is estimated by adding your average cycle length to the first day of your last period. The cycle length is measured from day 1 of one period to day 1 of the next.
For example, if your last period started on January 1 with a 28-day cycle, your next period is expected around January 29, with ovulation on approximately January 15.
Tip: Track your periods for at least 3–6 months to find your true average cycle length. Normal cycles range from 21 to 35 days.
Understanding Your Menstrual Cycle
The four phases of your monthly cycle
Your menstrual cycle has four distinct phases, each driven by different hormones:
Menstruation (Days 1–5)
The uterine lining sheds, resulting in your period. Day 1 of bleeding is day 1 of your cycle. Typically lasts 3–7 days.
Follicular Phase (Days 1–13)
FSH stimulates follicle growth. Estrogen rises, thickening the uterine lining. Overlaps with menstruation in the first days.
Ovulation (Day 14)
A surge in LH triggers egg release. The egg is viable for 12–24 hours. This is the most fertile day of your cycle.
Luteal Phase (Days 15–28)
Progesterone rises to maintain the uterine lining. If no fertilization occurs, hormone levels drop and menstruation begins.
Note: Day numbers shown are for a typical 28-day cycle. Your ovulation day shifts if your cycle is shorter or longer — the luteal phase stays approximately 14 days.
What Is the Safe Period?
Days when pregnancy is least likely in your cycle
The "safe period" refers to days in your cycle when pregnancy is least likely — the days outside your fertile window. For a 28-day cycle with a 5-day period:
Important: The calendar method is not a reliable form of birth control. Cycles can vary month to month, and sperm can survive up to 5 days. Always consult a healthcare provider for contraceptive advice.
When Is My Period Late?
Common causes and when to be concerned
A period is considered late if it hasn't started within 5 days of the expected date. Occasional delays of 1–2 days are normal. Common causes include:
When to act: If your period is more than 7 days late and you are sexually active, consider a pregnancy test. Consistently late or missed periods should be evaluated by a healthcare provider.
PMS: What to Expect Before Your Period
Symptoms that affect up to 75% of menstruating women
Premenstrual Syndrome (PMS) symptoms typically begin 7–10 days before your period during the luteal phase and resolve once menstruation starts.
Managing PMS: Regular exercise, balanced nutrition, adequate sleep, and stress reduction can help ease symptoms. Over-the-counter pain relievers can help with cramps. Consult your doctor if symptoms significantly affect daily life.
Assumptions & Limitations
What this calculator can and cannot do
Medical disclaimer: This calculator provides estimates for educational purposes. Always consult a healthcare professional for medical decisions regarding menstrual health, contraception, or fertility.
Frequently Asked Questions
Common questions about period tracking, cycle length, and menstrual health
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Last updated Feb 23, 2026