Enter the first day of your last menstrual period and cycle length - the calculator estimates your ovulation date, fertile window, and next period start.
The calculator estimates ovulation by using the first day of your last period and your average cycle length. It then shows an estimated fertile window, most fertile days and next period date.
The most fertile days are usually the days leading up to ovulation and the day of ovulation itself. Timing varies, especially if your cycles are irregular.
An ovulation calculator gives an estimate, not a guarantee. Ovulation can shift because of stress, illness, travel, breastfeeding, medication, hormonal changes or health conditions.
Pregnancy is most likely around ovulation, but fertile timing can vary and sperm can survive for several days. If you are avoiding pregnancy, do not rely on calculator estimates alone.
Ask for advice if your cycles are very irregular, absent, unusually painful, very heavy, or if you have been trying to conceive for 12 months without success, or 6 months if you are over 35.