Private cycle tool
Period Calculator
Predict your next periods, ovulation and fertile window — with calendar export, an irregular-cycle mode, and private notes. Free, no sign-up.
The date bleeding started most recently.
Cycle regularity
Typically 21–35. Default 28.
Typically 3–7.
Why this period calculator is different
| Feature | This tool | Typical free calculators |
|---|---|---|
| Works with no sign-up | Yes | Often app/login |
| Data stays in your browser | Yes | Usually tracked |
| Export dates to your calendar (.ics) | Yes | Rare |
| Irregular-cycle range mode | Yes | Rare |
| Private symptom notes | Yes | App only |
| Ad-free calculation area | Yes | Often ad-heavy |
How it works
Enter the first day of your last period and your cycle details. In regular mode the tool projects each next period by adding your average cycle length, estimates ovulation about 14 days before your next period, and marks a fertile window of roughly five days before ovulation through ovulation day. In irregular mode you give a shortest and longest cycle length, and each predicted period is shown as an earliest–latest date range.
Frequently asked questions
Is this period calculator accurate?
It is as accurate as the averages you enter, but real cycles vary due to stress, travel, illness, and other factors. Treat the dates as informed estimates.
Can I use the fertile window to avoid pregnancy?
No. Calendar-based estimates are not a reliable contraceptive method. Speak to a healthcare professional about contraception options.
What if my cycles are irregular?
Switch to irregular mode and enter your shortest and longest cycle length. Predictions become date ranges. Persistent irregularity is worth discussing with a clinician.
Is my data private?
Yes. All calculations happen in your browser. Your dates and notes are never sent to a server. If you tick “remember my inputs,” they are stored only on this device and you can clear them anytime.