Estimate fertile days
Timing rule
This calculator assumes ovulation happens about 14 days before the next period in an average cycle.
Reminder
The fertile window is shown as the five days before ovulation plus ovulation day and the following day.
How it works
The estimate starts from the first day of your last menstrual period and adds your average cycle length to project the next period. Ovulation is then estimated about 14 days before that projected date.
Because cycle length and ovulation timing can vary from month to month, these dates are only planning estimates. Use clinical advice or medical testing if you need more certainty.
This tool is not medical advice. It is meant for basic cycle awareness, planning, and understanding common fertility timing guidance.