Free Period Calculator Online
Calculate next period date, menstrual cycle length, period calendar, cycle day, ovulation estimate, fertile window, and cycle tracking dates with this free period calculator.
📅 Period Calculator
Live Cycle EstimatePeriod Inputs
Left SidePeriod Results
Right SideCycle Progress Pie Chart
| Cycle | Period Start | Period Window | Ovulation Estimate | Fertile Window |
|---|
The calculator estimates the next period from your average cycle length.
Tracking several cycles can improve your average estimate.
Cycle changes can happen. Ask a qualified clinician for health concerns.
What Is a Period Calculator?
A period calculator estimates the next period date, menstrual cycle day, period window, ovulation date, fertile window, and upcoming cycle calendar dates. It uses the first day of the last period, average cycle length, period length, and luteal phase length.
This free online menstrual cycle calculator is useful for cycle tracking, period planning, ovulation estimates, fertile window estimates, and creating a simple period calendar. Results are general estimates and can vary from real cycle patterns.
Next Period Calculator
Estimate your next period start date using last period date and cycle length.
Menstrual Cycle Calculator
Calculate cycle day, period window, and upcoming cycle calendar dates.
Ovulation Estimate
Estimate ovulation date using cycle length and luteal phase length.
Period Calendar
Generate multiple upcoming period windows and export them as a CSV file.
How Period Calculation Works
Period prediction starts with the first day of the last period and adds the average cycle length to estimate the next period. The period window uses your average period length. Ovulation is estimated by subtracting the luteal phase length from the next period date.
Period Calculator Formula
The calculator also estimates current cycle day by comparing the selected check date with the last period start date.
Period Date vs Cycle Day
The period date is an estimated calendar date for bleeding to begin. Cycle day counts the number of days since the first day of the last period. Cycle day 1 is the first day of the period.
Period Calculator Examples
Enter the last period date and 28-day cycle length to estimate the next period.
Use period length to estimate the start and end date of the next period.
Generate upcoming period and ovulation estimates for several cycles.
Benefits of Using a Period Calculator
Estimate upcoming period windows for personal planning.
Compare predicted dates with actual cycle dates over time.
Review estimated ovulation and fertile window dates.
Period Tracking Tips
- Track the first day of each period for several months.
- Use your average cycle length rather than a single cycle.
- Remember that stress, sleep, travel, health, and age can affect cycle timing.
- Speak with a qualified clinician for irregular cycles, pain, or health concerns.
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Frequently Asked Questions
Is this period calculator free?
Yes. You can estimate next period date, cycle day, period calendar, ovulation date, and fertile window for free.
How do I calculate my next period?
Add your average cycle length to the first day of your last period.
What is cycle day?
Cycle day counts from the first day of your last period. The first day of bleeding is cycle day 1.
Can this calculator estimate ovulation?
Yes. It estimates ovulation by subtracting the luteal phase length from the next period date.
Are period predictions exact?
No. They are estimates because cycle timing can vary from month to month.
Can I export the period calendar?
Yes. Use the Download CSV button to export estimated upcoming cycles.
Can cycle length change?
Yes. Cycle length can change due to health, stress, sleep, travel, age, and other factors.
Is this medical advice?
No. This calculator provides general estimates only and is not medical advice.