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

Nov 12, 2026

Cycle day 14

Fertile window

Nov 7 - Nov 13

6-day window

Next period

Nov 26, 2026

28-day cycle

Multi-cycle projection

Cycle	Period starts	Ovulation	Fertile window	Next period
1	Oct 29	Nov 12	Nov 7 - Nov 13	Nov 26
2	Nov 26	Dec 10	Dec 5 - Dec 11	Dec 24
3	Dec 24	Jan 7	Jan 2 - Jan 8	Jan 21

Cycle calendar

PeriodFertilePeakOvulation

October 2026

November 2026

December 2026

January 2027

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.

Related tools

Estimate your fertile window

Ovulation is when an ovary releases an egg. Pregnancy is only possible during a short span around it. If you're trying to conceive, knowing that span helps you time things. If you're avoiding pregnancy, it also matters, though a calculator isn't a reliable method of birth control.

Enter the first day of your last period and your usual cycle length. The tool estimates your ovulation date and fertile window.

How the estimate works

Ovulation usually happens about 14 days before the next period starts. In a 28-day cycle that's around day 14. In a 32-day cycle it's closer to day 18. The calculator counts back from your expected next period.

The fertile window is about six days: the five days before ovulation and the day of. Sperm can survive in the body for up to five days, while an egg lives roughly a day. That's why timing before ovulation counts.

When you can get pregnant

Mostly in that window, and chances are highest in the two days leading up to ovulation. Outside it, pregnancy is unlikely but not impossible. Cycles shift, and ovulation can come earlier or later than predicted, especially after illness, stress or travel.

Things that move ovulation

Stress, sleep changes, heavy exercise, big weight changes, illness and some medications can all push it. Conditions like PCOS or thyroid disorders affect it too. Breastfeeding and stopping hormonal birth control often lead to irregular cycles for a while.

If your cycles vary by more than a week, a calendar estimate loses accuracy. Pair it with other signs.

Cervical mucus that turns clear and stretchy
A rise in basal body temperature after ovulation
Positive result on an LH ovulation test strip
Mild one-sided pelvic pain in some people

When to see a doctor

If you've been trying for a year without success (six months if you're 35 or older), or your cycles are very irregular or absent, talk to a healthcare provider. They can check what's going on and offer help.

This tool is for information and not medical advice. Your dates stay in your browser.