Ovulation Calculator
Estimate your ovulation date and fertile window from your last period and cycle length.
- Estimated ovulationAug 7, 2026
- Fertile window opensAug 2, 2026
- Fertile window closesAug 8, 2026
- Next period expectedAug 21, 2026
Inputs used
- First day of last periodJul 24, 2026
- Average cycle length28 days
About this calculator
Ovulation typically happens about 14 days before the next period starts — not 14 days after the last one, which is why cycle length matters. The calculator takes the first day of your last period, adds your average cycle length, and counts back 14 days.
The fertile window spans roughly the five days before ovulation through the day after, because sperm can survive several days while the egg lives about one. If you're trying to conceive, the two or three days leading up to ovulation matter most.
Real cycles vary — stress, illness and travel all shift ovulation, and calendar estimates are least reliable for irregular cycles. Ovulation predictor kits or temperature tracking are more accurate. This is a general estimate, not contraception or medical advice.
Frequently asked questions
When do I ovulate?
Ovulation usually happens about 14 days before your next period starts, not 14 days after your last one. This calculator adds your average cycle length to the first day of your last period and counts back 14 days, so a 30-day cycle points to ovulation around day 16.
What is the fertile window?
It spans roughly the five days before ovulation through the day after, because sperm can survive several days in the reproductive tract while the egg lives only about one. The two or three days leading up to ovulation are the most fertile.
How reliable is this for irregular cycles?
Calendar estimates are least reliable when cycle length varies, since the prediction assumes a consistent cycle. If your cycles are irregular, ovulation predictor kits or basal body temperature tracking give a more accurate picture, and this estimate is not a form of contraception.
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Results are informational only — not financial, medical or legal advice.