Find your ovulation day and fertile window from your last menstrual period and average cycle length — with a visual fertility calendar marking your most fertile days.
Enter your data
Enter the first day of your last period, your average cycle length (usually 28 days) and how many days your period lasts.
The estimate assumes ovulation about 14 days before the next period. It is not a contraceptive method — real fertility varies from cycle to cycle.
Ovulation date: 15 January 2026The calendar marks your period, fertile window, ovulation day and the predicted start of your next period.
Indicative estimate, not medical advice. Ovulation is estimated as 14 days before the next period; fertility varies from cycle to cycle. It is not a contraceptive method — consult your doctor for family planning. Instant in-browser calculation, no account.
✚ Results are for informational purposes and do not replace medical advice. For health decisions, consult a doctor.
Ovulation is estimated 14 days before the next period, and the fertile window covers the days around it:
For a 28-day cycle, ovulation occurs around day 14, and the fertile window runs roughly from day 9 to day 15.
Ovulation usually occurs about 14 days before the next period. For a 28-day cycle, that is around day 14 from the start of the cycle.
It is the roughly 6-day span when the chance of conceiving is highest: the 5 days before ovulation plus ovulation day, since sperm can survive a few days.
The fertile days are those around ovulation. The calculator estimates them from your last period and cycle length, marking the fertile window.
Use your average cycle length, counted from the first day of one period to the first day of the next. A cycle between 21 and 35 days is considered normal.
It is indicative. The timing of ovulation can vary between cycles, especially if the cycle is irregular. Ovulation tests and temperature tracking give extra clues.
On the days of the fertile window, especially the 1–2 days before ovulation and on ovulation day. Outside this window the chance drops significantly.
For irregular cycles the calendar estimate is less precise. Ovulation tests, observing fertility signs and a medical consultation help for an accurate assessment.
Not necessarily. Ovulation is tied to the end of the cycle (about 14 days before the period), not the middle. For longer or shorter cycles, the ovulation day shifts accordingly.
The calendar highlights four things across the month(s): your period days, the fertile window (green), the single ovulation day (the most fertile day) and the predicted start of your next period. It turns the dates into an at-a-glance view so you can plan around your most fertile days.
Period (bleeding) length does not move the ovulation day — that is set by cycle length — but it marks how many days of your period and next period are shaded on the calendar. Set it to your usual number of bleeding days (often 3–7) for an accurate picture.