Period Calculator
Global Period Calculator
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Period Calculator & Counter

Enter your last period details to predict your next cycle and fertile window.

Next Period --
Ovulation Day --
Fertile Window --

Common Questions About Global Period Calculator

Learn more about your menstrual health and tracking.

How accurate is this prediction? +
This tool uses the standard calendar method. While accurate for many, your cycle can be affected by stress, illness, or lifestyle changes. It is intended for informational purposes only.
What is a normal cycle length? +
A normal cycle usually ranges between 21 and 35 days. The average cycle length is 28 days. If your cycle is consistently shorter or longer, consult a doctor.
When does ovulation usually occur? +
Ovulation typically happens about 14 days before your next period starts. This tool calculates your fertile window based on that 14-day window.
How does the reminder system work? +
We use your browser's local storage to remember your last entry. If you enable notifications, your browser will alert you 2 days before your expected period.
Is my data private? +
Yes. We do not store your data on any server. All calculations and saved data stay entirely on your own device within your browser.
What should I do if my period is irregular? +
If your cycle varies significantly every month, calendar tracking may be less reliable. We recommend keeping a manual log and discussing irregularities with a healthcare professional.
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