Ovulation Calculator
Estimate your ovulation day and fertile window from your last period and cycle length.
Enter your details below.
How to use
- Enter the first day of your last period.
- Enter your usual cycle length in days (often 28).
- Read your estimated ovulation day and fertile window.
About this tool
In a typical cycle, ovulation happens about 14 days before the next period, so this tool subtracts 14 from your cycle length and adds the result to the first day of your last period. The fertile window shown runs from five days before ovulation to one day after it, covering how long sperm and an egg can survive. The result is general information only, not medical advice, and it is unreliable for irregular cycles or as a contraceptive method.
Frequently asked questions
Is ovulation always on day 14?
No — day 14 assumes a 28-day cycle. With a longer or shorter cycle, ovulation shifts, which is why the tool uses your own cycle length.
Can this be used to avoid pregnancy?
No — cycle timing alone is not reliable contraception, especially with irregular cycles, stress, or illness shifting ovulation.