Period Calculator
Predict your next period and a 6-month cycle calendar
Menstrual Calendar
Predicted periods, ovulation day and fertile window for each cycle, based on the values you entered.
Free Period Calculator – Menstrual Calendar
Next period date, 6-month calendar, ovulation and fertile days
This period calculator uses the first day of your last period together with your cycle and period length to predict when your next period starts and to build a menstrual calendar for the months ahead. Each cycle also lists the estimated ovulation day (14 days before the next period) and the fertile window. If you enter a past date the tool finds the cycle you are in now and shows which day of the cycle today is. Your dates stay on your device; results are calendar-method estimates.
Features
6-Month Calendar
3, 6 or 12 months of periods and ovulation days
Next Period
Days until it starts and the estimated end date
Fertile Days
Ovulation and fertile window for every cycle
Private
Your dates are stored only on your device
Cycle Facts
How it is calculated
- Next period = last period + cycle length
- Ovulation ≈ next period − 14 days
- Fertile window: ovulation −5 … +1 days
- A normal cycle is 21–35 days; a period lasts 2–7 days
When to see a doctor
- Cycles shorter than 21 or longer than 35 days
- Periods lasting more than 7 days
- No period for more than 3 months
- Severe pain or very heavy bleeding
Frequently Asked Questions
When is my next period?
Add your cycle length to the first day of your last period: with a 28-day cycle, a period that started on March 1 is followed by one on March 29. The calculator does this for you and lists the following cycles too.
How do I work out how late my period is?
Count the days since the expected start date. A few days late is common after stress, illness or travel; if you are more than a week late, a pregnancy test is recommended.
How do I find my cycle length?
It is the number of days from the first day of one period to the first day of the next. An average over several months is most accurate; if you are unsure, start with 28.
Can I use this for birth control?
No. The calendar method is an estimate and is not a reliable form of contraception. The tool is for information only.
Why does it show ovulation?
Seeing fertile days next to the period calendar helps those planning a pregnancy. For a detailed calculation use the ovulation calculator.