Ovulation Calculator
Estimate your fertile window and ovulation date based on your last menstrual period and average cycle length.
Published by:
isCalculator Editorial Team
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How to use this tool?
How to Use the Ovulation Calculator
This tool estimates your ovulation date, fertile window, and next period based on your cycle details. Follow these steps:
- Enter the first day of your last period – Select the exact date from the calendar picker.
- Set your average cycle length – Input the number of days from the start of one period to the next (typically 21–35 days). The default is 28.
- Specify your period length – Enter how many days your period usually lasts (usually 3–7 days). The default is 5.
- Adjust your luteal phase length – This is the time from ovulation to your next period (typically 12–16 days). The default is 14.
- Click Calculate to see your results.
Results explained:
- Ovulation Date – The day you are most likely to ovulate.
- Fertile Window – The 6-day period (5 days before ovulation plus ovulation day) when conception is most likely.
- Next Period – The estimated start date of your next menstrual period.
Note: All dates are calculated assuming a consistent cycle length. For irregular cycles, results may vary.
Previous Results
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Frequently Asked Questions
Ovulation date is estimated by subtracting the luteal phase length from the cycle length and adding that to the first day of your last period.
The fertile window is the 6-day period ending on the day of ovulation, including the 5 days before ovulation and the day itself.
This calculator provides an estimate based on average cycle lengths. Individual cycles may vary. For best results, track your cycle over several months.
