Ovulation calculator●
Estimate your ovulation day and fertile window from the first day of your last period and your cycle length.
Enter the first day of your last period. The result updates as you change a value. Nothing leaves this page.
Result
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Your coming cycles
| Cycle starts | Fertile window | Ovulation | Next period |
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The dates you enter are used only in this browser tab. Nothing is sent, saved or tracked.
How the ovulation date and fertile window are worked out
Ovulation happens when an ovary releases an egg, usually about 14 days before the next period starts. The calculator counts your cycle length from the first day of your last period to find the day your next period is due, then subtracts your luteal phase (the time between ovulation and the period, 14 days by default). With a 28 day cycle that puts ovulation on day 14 after your period began. The egg lives for about 12 to 24 hours, but sperm can survive for up to 5 days, so the fertile window runs from 5 days before ovulation to the day of ovulation itself. The 2 days before ovulation and the day of ovulation are the most fertile. If you conceive, a pregnancy test is most reliable from the day your period is due, and the due date is about 266 days after ovulation. If your cycles are irregular, treat the dates as a rough guide and look for body signs such as cervical mucus or use ovulation test strips to confirm.
Pregnancy due date calculator →Common questions
How do I calculate my ovulation day?
Count your cycle length from the first day of your last period to find when the next one is due, then go back 14 days. With a 28 day cycle ovulation falls on day 14. A shorter or longer cycle moves it earlier or later.
How long is the fertile window?
About six days: the 5 days before ovulation and the day of ovulation. Sperm can live up to 5 days, the egg only 12 to 24 hours, so having sex in the days before ovulation matters most.
Which days are the most fertile?
The two days before ovulation and the day of ovulation. These are shown as the most fertile days in the result.
What if my cycle is irregular?
Use your average cycle length, but expect the real date to move by several days. Ovulation test strips, basal body temperature and cervical mucus give a more reliable signal than a calendar.
When can I take a pregnancy test?
From the day your period is due, which is the Pregnancy test from date in the result. Testing earlier can give a false negative.
Can I use this as birth control?
No. Ovulation can come earlier or later than predicted and sperm can survive for days, so a calendar estimate is not a reliable way to prevent pregnancy.
Is my information stored?
No. The dates stay in your browser tab and are never sent or saved.