Health & Fitness
Ovulation Calculator
Find your most fertile days and estimated ovulation date for the next few cycles, calculated privately in your browser.
Ovulation & fertile window
Enter the first day of your last period to see your fertile window.
Understanding your fertile window
Each cycle has a short window when conception is possible. Because sperm can live for up to five days and the released egg survives for about a day, the days leading up to ovulation matter most. Tracking your cycle length over a few months makes these estimates more accurate. If you are trying to conceive, timing intercourse within the fertile window gives the best chance each cycle.
Frequently asked questions
- When am I most fertile?
- Your fertile window is the roughly six days ending on the day of ovulation. The highest chance of conception is in the two to three days just before ovulation, because sperm can survive for several days while an egg lives for about 24 hours.
- How is ovulation estimated?
- Ovulation usually happens about 14 days before your next period. We estimate it by subtracting your luteal phase length from your cycle length and counting forward from the first day of your last period.
- Is this reliable for avoiding pregnancy?
- No. Calendar estimates are useful for planning but should not be relied on as contraception, because cycles vary and ovulation can shift. Speak with a healthcare provider about reliable birth control.
- What is the luteal phase?
- The luteal phase is the time between ovulation and your next period, typically 12–14 days and fairly consistent for each person. If you know yours, entering it gives a more accurate ovulation estimate.