Ovulation Calculator
Estimate your next ovulation date and fertile window from your last period and typical cycle length.
How this estimate works
Ovulation typically happens about 14 days before the next period starts, regardless of total cycle length. The fertile window covers the 5 days before ovulation plus ovulation day itself, since sperm can survive that long. Cycles vary naturally, so treat this as a general estimate rather than a precise prediction — tracking a few real cycles improves accuracy.
About the Ovulation Calculator
The Ovulation Calculator estimates your likely ovulation date and fertile window from the first day of your last period and your average cycle length. It helps when planning or tracking a cycle.
Ovulation usually occurs about 14 days before the next period starts, so in a 28-day cycle it is around day 14, but cycles vary. The fertile window covers roughly the five days before ovulation and the day itself, because sperm can survive for several days. This is an estimate based on averages; irregular cycles, stress and illness can shift ovulation. It is not a method of contraception.
How to use it
- Enter the first day of your last period.
- Enter your average cycle length in days.
- Read the estimated ovulation date and fertile window.
- Track several cycles for better accuracy.
Tips and good to know
- Ovulation tests and body temperature tracking give more precise information.
- Cycle length is counted from day 1 of one period to day 1 of the next.
- See a doctor if cycles are very irregular or if you have concerns.
Frequently asked questions
Can I use it to avoid pregnancy?
No, it is not reliable for contraception.
Why is my result different from my app?
Methods and assumptions differ.
Is it medical advice?
No.