Ovulation calculator to estimate your ovulation date, fertile window, most fertile days, and next period date from your period start date and menstrual cycle length.
Use this ovulation calculator to estimate your ovulation date, fertile window, and most fertile days based on the first day of your last period and your usual cycle length.
It can also estimate your next period date, which makes it useful for cycle tracking, family planning, and getting a general idea of when conception is most likely. The result is an estimate only, because real ovulation timing can vary from cycle to cycle.
First day of your last menstrual period
Number of days in your cycle
days
Result
Your ovulation date
- Estimated ovulation date:
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- Most fertile days:
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- Fertile window:
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- Estimated next period date:
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Upcoming cycle estimates
| Cycle |
Ovulation |
Fertile window |
Next period |
Estimated ovulation calendar
Fertile window
Ovulation
Related calculators
This calculator provides an estimate only and may be inaccurate. Cycle length, ovulation timing, and period dates can vary.
Ovulation Calculator FAQ
How does this ovulation calculator work?
It estimates ovulation from the first day of your last menstrual period and your cycle length. It then shows your estimated ovulation date, fertile window, most fertile days, and next period date.
When does ovulation usually happen?
Ovulation often happens about 14 days before the next period, not always on day 14 of the cycle. In a 28-day cycle, that is commonly around day 14, but in longer or shorter cycles it shifts.
What is the fertile window?
The fertile window is the group of days when pregnancy is most likely. It usually includes the 5 days before ovulation and the day of ovulation, because sperm can survive for several days while the egg is available for a shorter time.
What are the most fertile days?
The highest chance of conception is usually on the day before ovulation and the day of ovulation. This calculator highlights those days separately from the wider fertile window.
Can I use cycle length to predict my next period?
Yes. If your cycle is reasonably regular, the next period can be estimated as period start date + cycle length. This calculator uses that approach to show your expected next period date.
How accurate is an ovulation calculator?
It gives an estimate only. Real ovulation can vary because of stress, illness, irregular cycles, hormone changes, travel, and many other factors. It should not replace medical advice or clinical fertility tracking.
