Fertile Window Calculator
Estimate the range of days when conception is most likely, based on your last period and average cycle length. This is a calendar estimate, not a test of fertility.
Your cycle details
Your estimate
Enter your cycle details to see an estimate.
How this estimate is calculated
The calculator estimates ovulation as about 14 days before your next expected period. It then shows a fertile window from five days before ovulation through one day after.
The window is wider than the day of ovulation because sperm can survive for several days in the reproductive tract, while an egg is viable for roughly 12–24 hours. The exact timing varies from person to person and from cycle to cycle.
For a closer look at calendar estimates and body signs, read ovulation signs and your fertile window.
What this tool cannot tell you
- Whether ovulation actually occurred
- Whether a specific day is fertile for you
- Whether you have a fertility concern
- Whether it is safe to rely on this for contraception
Do not use calendar-based predictions to prevent pregnancy. They cannot reliably identify days when conception is impossible.
Questions about the fertile window
What is the fertile window?
It is the range of days around ovulation when conception is most likely. Because sperm can survive for several days and an egg is viable for roughly 12–24 hours, the window includes the days before ovulation as well as the day after.
Can I get pregnant outside the estimated window?
The estimate may not match your actual cycle. Ovulation can happen earlier or later than predicted, so treat the window as a best guess rather than a boundary. If you are trying to conceive or avoid pregnancy, discuss reliable methods with a healthcare professional.
Is this reliable for avoiding pregnancy?
No. Calendar-based methods are not a reliable form of contraception. They do not account for cycle variation and cannot confirm when ovulation occurs.
General references
These organizations provide general health information. They are external sites with their own content and policies, and this site is not affiliated with them.