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Period & Ovulation Predictor
Project the next 12 cycles, see ovulation and fertile window dates, and plan ahead — math only, no account.
How a menstrual cycle works
The textbook menstrual cycle lasts 28 days but anything between 21 and 35 days is considered normal in adults. Cycle day 1 is the first day of bleeding. Around day 14 the ovary releases an egg; the corpus luteum then produces progesterone for roughly 14 ± 1 days, regardless of total cycle length, until either pregnancy occurs or the uterine lining sheds and a new cycle begins. The fertile window covers the five days before ovulation plus ovulation day itself because sperm survive up to five days inside the reproductive tract. Tracking lets you anticipate menses, recognise unusual variation early and plan trips, exams and competitions around symptom-heavy days. The math here is calendar-based: it cannot detect the hormonal signs (basal body temperature, cervical mucus, LH surge) that confirm ovulation in real time.
How to use the predictor
- Pick the first day of your last period — Use the first day with real bleeding, not spotting. The calculator builds the next 12 cycles from this anchor.
- Enter your average cycle length — If your cycles vary, average the last six. If you have no idea, leave the default (28 days). Anything outside 20–45 days is treated as out of scope.
- Set the bleeding length — How many days you usually bleed (2–10). The schedule shades both the start and end of each upcoming period.
- Read the calendar — The table shows 12 future cycles with start, end, PMS window and fertile window. Add them to your calendar from the date column.
How the dates are projected
Next period start = last period + cycle length. Ovulation = next period − 14 days. Fertile window = ovulation − 5 to ovulation + 1. PMS window = next period − 7 to next period − 1. The 14-day luteal phase is biological; cycle variation comes from the follicular phase before ovulation.
12-cycle forecast
Each row is one upcoming cycle. The table is generated client-side from your inputs — nothing is stored. Use the columns to add events to your phone calendar.
| # | Start | End | PMS window | Fertile window |
|---|