This calculator estimates your fertile window and the most likely day of ovulation from the first day of your last period and your average cycle length. It uses the standard model where ovulation occurs about 14 days before the next period starts, and the fertile window spans roughly the five days before ovulation plus the day itself, reflecting how long sperm and the egg can survive. Enter the date your last period began and your typical cycle length in days, and the tool marks the estimated ovulation date and fertile range. Cycles vary from month to month and person to person, so these dates are approximate and not a reliable method of contraception or a guarantee of conception. Everything is calculated locally in your browser with nothing sent anywhere. This is general information only, not medical advice, so consult a healthcare provider for family planning.
It assumes ovulation happens about 14 days before the next period, so it counts back from the projected period based on your cycle length.
It is the span of about six days ending on ovulation day, reflecting how long sperm can survive plus the egg being viable.
It is an estimate based on a regular cycle, so it is less precise for irregular cycles and is not a form of contraception.
This calculator estimates your fertile window and the most likely day of ovulation from the first day of your last period and your average cycle length. It uses the standard model where ovulation occurs about 14 days before the next period starts, and the fertile window spans roughly the five days before ovulation plus the day itself, reflecting how long sperm and the egg can survive.
Yes. Ovulation Window Calculator is completely free, with no sign-up and no usage limits.
Yes. Ovulation Window Calculator runs in any modern web browser. There is nothing to download or install.
Yes. Ovulation Window Calculator runs entirely on your device in your browser, so nothing you enter is uploaded to a server.