Ovulation Calculator
Estimate ovulation day, fertile window and next periods for the coming cycles.
How to use the Ovulation Calculator
- 1Enter the first day of your last period.
- 2Set your average cycle length, period length and luteal phase.
- 3See your ovulation day, fertile window and next periods in the calendar.
About Ovulation Calculator
The Ovulation Calculator estimates when you ovulate and on which days you are most likely to conceive. Enter the first day of your last period and your average cycle length from 21 to 45 days. Ovulation is placed one luteal phase before the next period; the luteal phase is 14 days by default and can be set from 10 to 16 days if you know yours from ovulation tests or temperature charting.
The result shows the next ovulation date, the fertile window from five days before ovulation to one day after, the date of the next period and the days left until ovulation. A month calendar marks period days, fertile days and the ovulation day and can be paged forward, and a table lists ovulation, fertile window and period dates for the next six cycles. The dates are estimates and not a method of contraception.
It is used by people trying to get pregnant who want to time intercourse, and by anyone who wants to know when their next period is due. Once pregnant, the Pregnancy Due Date Calculator works out the due date from the same last-period date.
Frequently asked questions
How do I calculate my ovulation day?
Subtract the luteal phase, usually 14 days, from your cycle length. In a 28-day cycle ovulation happens around day 14; in a 32-day cycle around day 18, counting the first day of the period as day 1.
How long is the fertile window?
About six days: the five days before ovulation and the day of ovulation, because sperm can survive up to five days and the egg about 12 to 24 hours. The chance of pregnancy is highest in the two days before ovulation.
What is the luteal phase?
The luteal phase is the time from ovulation to the next period. It is fairly constant for each person, usually 12 to 14 days, so differences in cycle length mostly come from the phase before ovulation.
Can I use an ovulation calculator for birth control?
No. Ovulation can shift from cycle to cycle, so a calendar estimate is not a reliable contraceptive method.
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