Estimate an approximate ovulation day and fertile window based on the first day of your last period and your average cycle length. This is a rough estimate only and should not be used as birth control or medical advice.
This should be the first day of your most recent menstrual bleeding.
Many people have cycles around 28 days, but 21–35 days is common. Use your own average if you know it.
Important: This tool is for general information only and is based on typical cycle patterns (ovulation often occurs about 12–16 days before the next period). Actual ovulation can vary month to month and between individuals. Do not use this calculator alone to avoid pregnancy or to diagnose any condition. For personalized guidance, speak with a qualified healthcare professional.