Ovulation Calculator
Calculate your ovulation day and fertile window online free from your last period and cycle length. Free online ovulation calculator for the next cycles.
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How to use Ovulation Calculator
- 1Enter the first day of your last period and your average cycle length (28 days if you are not sure)
- 2Adjust the luteal phase if you know it (14 days is typical)
- 3Click Calculate fertile days to see your fertile window, ovulation day, next period, test day and the next 4 cycles
Frequently asked questions
How is ovulation calculated?▾
Ovulation usually happens about 14 days before the next period (the luteal phase). With a 28-day cycle that is around day 14; with a 32-day cycle around day 18. The calculator subtracts your luteal phase from your next expected period.
What is the fertile window?▾
The six days ending on ovulation day plus the day after. Sperm can survive up to five days, and the egg about 12–24 hours, so the two to three days before ovulation are the most fertile.
When should I take a pregnancy test?▾
Most home tests are reliable from the day your period is due, about 14 days after ovulation. Testing earlier can give a false negative.
Does it work with irregular periods?▾
It assumes a regular cycle. If your cycle varies, use your average length and treat the dates as a rough guide; ovulation predictor kits (LH tests) or basal body temperature tracking are more reliable.
Can I use this for birth control?▾
No. Calendar estimates are not reliable enough to prevent pregnancy.
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