Enter the first day of your last period and your usual cycle length, and this ovulation calculator estimates when you are most likely to ovulate, your fertile window, when your next period is due and the earliest day a home pregnancy test is likely to work. A table shows the same dates for the next six cycles so you can plan ahead.
Ovulation usually happens about 14 days before the next period, not on day 14 of every cycle, so the calculator uses your cycle length and an adjustable luteal phase. Nothing you enter is stored or sent anywhere. The results are estimates, not a diagnosis or a method of contraception.
How to use the Ovulation Calculator tool
- Choose the first day of your last period.
- Enter your average cycle length (from the first day of one period to the first day of the next).
- Leave the luteal phase at 14 days unless you know yours.
- Read your next ovulation date, fertile window and next period.
- Scroll the table for the next six cycles.
Why use ToolOrca Ovulation Calculator
- Ovulation date and fertile window
- Next period and pregnancy test date
- Estimated due date if you conceive
- Six cycles ahead
- Adjustable cycle and luteal phase
- Private: nothing is saved
How the fertile window is calculated
The egg lives for about 12–24 hours after ovulation, but sperm can survive up to five days. Your fertile window is therefore the five days before ovulation plus the day of ovulation and the day after. Ovulation is estimated as cycle length minus luteal phase days after the first day of your period: day 14 in a 28-day cycle, day 21 in a 35-day cycle.
Signs such as clearer, stretchy cervical mucus, a small rise in basal body temperature after ovulation and positive ovulation (LH) test strips can confirm the timing more precisely than a calendar.
Frequently asked questions
When do I ovulate with a 28-day cycle?
Usually around day 14, counting the first day of your period as day 1. Your most fertile days are about days 9 to 15.
What if my cycles are irregular?
Use your average cycle length, but treat the dates as rough guides. Ovulation test strips or tracking body temperature give a better picture when cycles vary a lot.
When can I take a pregnancy test?
Most home tests are reliable from the day your period is due, about 14 days after ovulation. Testing earlier can give a false negative.
Can I use this to avoid pregnancy?
No. Calendar estimates are not reliable enough to use as contraception, because ovulation can shift from cycle to cycle.
How is the due date estimated?
By adding 266 days (38 weeks) to the ovulation date, which equals 40 weeks from the last period in a 28-day cycle. See the due date calculator for more detail.