Period Calculator
A period (menstrual cycle) calculator predicts future menstruation dates based on cycle length and period duration. The average cycle is 28 days, but cycles from 21 to 35 days are normal. Tracking helps identify irregularities and plan around key life events.
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Tip: Cycle irregularity of a few days is normal. Consult a doctor if cycles are consistently shorter than 21 days, longer than 35 days, or if you experience very heavy bleeding.
- 1Record the first day of your last period (day 1)
- 2Add cycle length to find the next period start date
- 3Add period length to find the end date
- 4Repeat for subsequent cycles
| Phase | Days (28-day cycle) | Key Events |
|---|---|---|
| Menstruation | 1–5 | Uterine lining sheds |
| Follicular | 1–13 | Follicles develop in ovaries |
| Ovulation | ~14 | Egg released — peak fertility |
| Luteal | 15–28 | Progesterone rises; PMS may occur |
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Fun Fact
The word "menstruation" comes from Latin "mensis" (month) and Greek "mene" (moon). Many ancient calendars were based on the lunar cycle (~29.5 days), close to the average menstrual cycle.
References
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