Use this free ovulation calculator and fertility tracker to pinpoint your most fertile days, estimated ovulation date, and next period date based on your cycle length.
How to use this calculator
Enter the first day of your last menstrual period.
Specify your average menstrual cycle length in days (default is 28 days).
View your estimated ovulation date, peak fertile window, and upcoming period start date.
Formula & method
Fertile Window & Luteal Phase Formula
Ovulation Date = (Last Period + Cycle Length) − 14 days
Fertile Window = Ovulation Date − 5 days to Ovulation Date + 1 day.
Example
Last period Jan 1 with 28-day cycle: Next period Jan 29. Ovulation = Jan 15. Fertile window = Jan 10 to Jan 16.
Key insights
Ovulation typically occurs 14 days before the start of the next menstrual period (luteal phase length).
The fertile window includes the 5 days before ovulation plus ovulation day, because sperm can survive up to 5 days in the reproductive tract.
Peak fertility occurs during the 2 days leading up to and including ovulation day.
Tracking basal body temperature and cervical mucus can confirm ovulation timing.
How to interpret your result
Ovulation Date
The estimated day an egg is released from the ovary.
Fertile Window
The 6-day span during which intercourse is most likely to result in pregnancy.
Peak Fertility
The 48-hour period with the absolute highest probability of conception.
Frequently asked questions
When am I most fertile?
You are most fertile during the 2 days before ovulation and the day of ovulation itself.
Can I use this as a period tracker?
Yes. The tool calculates your next expected period date based on your average cycle length.
Is cycle length always 28 days?
No. Normal cycle length ranges from 21 to 35 days in healthy adults.
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Pregnancy Calculator — Estimate your due date, current gestational age and trimester progress.