Ovulation Calculator

Find your fertile window and ovulation date based on your menstrual cycle.

Enter your last period date above to calculate your ovulation window

How ovulation is calculated

Ovulation typically occurs 14 days before your next period. For a 28-day cycle, that's day 14. For a 32-day cycle, it's day 18.

Ovulation Day
Ovulation = LMP + (Cycle Length − 14)
Example: LMP June 1, 28-day cycle → Ovulation on June 15
Fertile Window
5 days: Ovulation day ± 2 days + day before
Sperm can survive up to 5 days in the female reproductive tract

The four cycle phases

Menstrual Phase

Day 1–5 (average). Uterine lining sheds. Hormone levels are at their lowest.

Follicular Phase

Day 1–13. Estrogen rises, follicles develop in the ovary, uterine lining thickens.

Ovulation Phase

Around day 14. LH surge triggers egg release. Peak fertility. Lasts 12–24 hours.

Luteal Phase

Day 15–28. Progesterone rises to prepare uterus for implantation. Drops if no pregnancy.

Frequently asked questions

How accurate is this ovulation calculator?

This calculator gives an estimate based on average cycle patterns. It assumes a consistent cycle length and that ovulation occurs 14 days before the next period. In reality, ovulation can vary by several days due to stress, illness, travel, or hormonal changes. For precise tracking, use ovulation predictor kits (OPKs) or basal body temperature monitoring.

What is the fertile window?

The fertile window is the 5–6 days during which pregnancy is possible: the 5 days before ovulation and the day of ovulation itself. An egg survives 12–24 hours after ovulation, but sperm can live up to 5 days in the reproductive tract, so sex before ovulation can still lead to pregnancy.

My cycle is irregular. Can I still use this?

This calculator works best for regular cycles between 21–35 days. If your cycles vary significantly, use the average of your last 3–6 cycles as input. For highly irregular cycles (PCOS, perimenopause), consult a gynaecologist for personalised tracking methods.

What cycle length should I enter?

Count from the first day of one period to the first day of the next period. A typical range is 21–35 days, with 28 days being average. Track 2–3 cycles to get your personal average.

Can I use this to avoid pregnancy?

This calculator is intended as an educational tool, not as contraception. The fertile window prediction has significant uncertainty. For reliable birth control, consult a healthcare provider about evidence-based contraceptive methods.