Ovulation Calculator Please select the first day of your last menstrual period: JanuaryFebruaryMarchAprilMayJuneJulyAugustSeptemberOctoberNovemberDecember / 12345678910111213141516171819202122232425262728293031 / 2023202420252026202720282029203020312032203320342035203620372038203920402041204220432044204520462047204820492050 Usual number of days in your cycle: 2021222324252627282930313233343536373839404142434445 Menstrual periods are different from woman to woman and month to month. Use this calculator to see when you may be ovulating to help find your most fertile days.