Ovulation typically occurs 14 days before your next period, regardless of cycle length. For a 28-day cycle that means day 14; for a 32-day cycle it is around day 18. Your fertile window begins 5 days before ovulation and ends 1 day after.

How long is the fertile window?

The fertile window is typically 6 days: the 5 days before ovulation (when sperm can survive in the reproductive tract) plus the day of ovulation itself. Peak fertility is the 2 days just before ovulation.

Can I get pregnant outside the fertile window?

Pregnancy is only possible during the fertile window. However, predicting the window from calendar data alone is imprecise; cycles vary month to month. Ovulation predictor kits (OPKs) or basal body temperature tracking provide more reliable confirmation.

What affects ovulation timing?

Stress, illness, significant weight changes, and hormonal conditions such as PCOS can shift ovulation earlier or later in a cycle. If your cycle length varies by more than a few days month to month, calendar-based predictions become less reliable.

Ovulation Calculator

Calculate your ovulation date and fertile window. View a color-coded calendar of your most fertile days across multiple cycles.

First day of last periodAverage cycle length (days)

Period duration (days)Luteal phase (days)Cycles to show

Ovulation date

Sep 30, 2026

Cycle day 14

Fertile window

Sep 25 - Oct 1

6-day window

Next period

Oct 14, 2026

28-day cycle

Multi-cycle projection

Cycle	Period starts	Ovulation	Fertile window	Next period
1	Sep 16	Sep 30	Sep 25 - Oct 1	Oct 14
2	Oct 14	Oct 28	Oct 23 - Oct 29	Nov 11
3	Nov 11	Nov 25	Nov 20 - Nov 26	Dec 9

Cycle calendar

PeriodFertilePeakOvulation

September 2026

October 2026

November 2026

December 2026

This calculator estimates fertility windows based on average cycle patterns. Actual ovulation varies. Consult a healthcare provider for family planning guidance.

How does the Ovulation Calculator work step by step?

This calculator estimates your ovulation date and fertile window based on the calendar method. Ovulation typically occurs a fixed number of days before your next period, determined by your luteal phase length (default 14 days). The formula is: ovulation day = cycle day (cycle length minus luteal phase). For a 28-day cycle with a 14-day luteal phase, ovulation falls on day 14. The fertile window spans 6 days: from 5 days before ovulation (because sperm can survive up to 5 days in the reproductive tract) through the day after ovulation (the egg remains viable for roughly 24 hours). Peak fertility is the 2 days immediately before and on ovulation day. The calculator projects these windows across multiple cycles so you can plan ahead.

What does a typical Ovulation Calculator result look like?

For a last period starting January 1 with a 28-day cycle and 14-day luteal phase: ovulation falls on January 15 (day 14). The fertile window runs January 10 through January 16. Peak fertility is January 14 and 15. The next period is expected January 29. Cycle 2 would start January 29 with ovulation on February 12, and cycle 3 starts February 26 with ovulation on March 12.

Frequently asked questions

When do I ovulate?
Ovulation typically occurs 14 days before your next period, regardless of cycle length. For a 28-day cycle that means day 14; for a 32-day cycle it is around day 18. Your fertile window begins 5 days before ovulation and ends 1 day after.
How long is the fertile window?
The fertile window is typically 6 days: the 5 days before ovulation (when sperm can survive in the reproductive tract) plus the day of ovulation itself. Peak fertility is the 2 days just before ovulation.
Can I get pregnant outside the fertile window?
Pregnancy is only possible during the fertile window. However, predicting the window from calendar data alone is imprecise; cycles vary month to month. Ovulation predictor kits (OPKs) or basal body temperature tracking provide more reliable confirmation.
What affects ovulation timing?
Stress, illness, significant weight changes, and hormonal conditions such as PCOS can shift ovulation earlier or later in a cycle. If your cycle length varies by more than a few days month to month, calendar-based predictions become less reliable.