How to Calculate Ovulation and Your Fertile Window

Knowing when you ovulate helps if you are trying to conceive or simply want to understand your cycle. Predict your dates with the period calculator.

Step 1: Know your cycle length

Count from the first day of one period to the day before the next. Track 3–6 cycles and take the average. 21–35 days is normal for adults.

Step 2: Find ovulation

Ovulation usually happens about 14 days before your next period. In a 28-day cycle that is day 14; in a 32-day cycle, around day 18.

Step 3: Your fertile window

Sperm can live up to 5 days and an egg about 24 hours, so the fertile window is roughly the 5 days before ovulation, ovulation day and the day after.

Signs of ovulation

• Clear, stretchy cervical mucus.
• A small rise in basal body temperature after ovulation.
• Positive ovulation (LH) test.
• Mild one-sided pelvic pain for some people.

When to see a doctor

If cycles are very irregular, under 21 or over 35 days, or you have been trying to conceive for 12 months (6 months if over 35).