Estimate ovulation timing and a broad fertile window from cycle length and LMP. Calendar estimates are not guaranteed contraception.
Estimate an ovulation date and a broad fertile-window range from cycle length and the first day of the last period. Ovulation Calculator uses a calendar estimate based on an assumed luteal phase. Real ovulation can vary between cycles, so the result should not be used as a guaranteed contraception or fertility method. How to use Ovulation Calculator: Enter the first day of the last menstrual period. Enter the usual cycle length. Review the estimated ovulation date and fertile window, then consider appropriate clinical or fertility-tracking methods if needed. Common uses: Cycle planning General fertility education Preparing questions for a clinician Is ovulation always on day 14? No. The calendar estimate changes with cycle length and real ovulation can vary. Is this a contraception method? No. A calendar estimate should not be treated as guaranteed contraception. Can fertility signs improve timing? Yes. Clinical guidance may incorporate additional signs or testing beyond a calendar calculation.