Enter the first day of your last period, how long it lasted, and your cycle length — the calculator estimates your next period, ovulation date, and fertile window.
The calculator estimates your next period, ovulation date and fertile window from the first day of your last period, your usual period length and your average cycle length. It is an estimate, not a medical diagnosis.
A calculator can be helpful if your cycles are fairly regular, but ovulation and period timing can shift because of stress, illness, travel, breastfeeding, medication, hormonal contraception or health conditions.
Many adult cycles are around 21-35 days, but individual patterns vary. A cycle is counted from the first day of one period to the first day of the next period.
Do not rely on calculator estimates alone to prevent pregnancy. Fertile windows can shift, and sperm can survive for several days. Speak with a healthcare professional about reliable contraception.
Ask for medical advice if your periods are very heavy, very painful, suddenly irregular, absent for several months, shorter than 21 days or longer than 35-40 days, or if you have bleeding between periods.