FREE TOOL
Ovulation Calculator
Calculate your estimated ovulation date and fertile window based on your cycle length and last period.
Ovulation Date
Jul 19, 2026
Fertile Window
Jul 14, 2026 - Jul 20, 2026
Cycle Day View
Next 3 Periods
Period 1: Aug 2, 2026 (Sun)
Period 2: Aug 30, 2026 (Sun)
Period 3: Sep 27, 2026 (Sun)
Why Use Our Ovulation Calculator?
Ovulation Date Calculation
Estimates ovulation day based on your last period and cycle length using the standard LH surge timing method.
Fertile Window Display
Shows the five days before ovulation plus the day after - the full fertile window when conception is most likely.
Adjustable Cycle Length
Enter your actual cycle length from 21 to 35 days for a more personalized estimate than a fixed 28-day assumption.
Visual Cycle Calendar
A color-coded day grid shows each phase of your cycle - period days, fertile window, and ovulation day at a glance.
Next Three Periods
Predicts the start dates of your next three periods based on your cycle length so you can plan ahead.
100% Private
Your dates are never sent to any server. All calculation happens locally in your browser.
Frequently Asked Questions
How is ovulation date calculated?
Ovulation typically occurs 14 days before the next period. The calculator subtracts 14 from your cycle length and adds that to the first day of your last period.
What is the fertile window?
The fertile window is the 5 days before ovulation plus the day of ovulation and the day after - the days when conception is most likely because sperm can survive up to 5 days.
How accurate is this calculator?
It is an estimate based on average cycle patterns. Actual ovulation varies based on stress, illness, and hormonal changes. An ovulation test kit provides more accurate real-time detection.
What cycle length should I enter?
Enter your typical cycle length from the first day of one period to the first day of the next. The average is 28 days, but normal cycles range from 21 to 35 days.
What if my cycle is irregular?
This calculator works best for regular cycles. If your cycle varies significantly, the fertile window estimate will be less accurate. Tracking with OPK tests is recommended.
Is this ovulation calculator free?
Yes. Completely free with no account or sign-up required.
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