Ovulation Calculator
Estimate your ovulation date and most fertile days from your cycle.
Updated
How the Fertile Window Is Estimated
Ovulation typically happens about 14 days before your next period starts — not 14 days after your last one. That distinction matters if your cycles aren't exactly 28 days. This calculator takes your cycle length, subtracts the typical 14-day luteal phase, and counts forward from the first day of your last period.
The fertile window spans roughly the five days before ovulation plus ovulation day itself, because sperm can survive up to five days while the egg lives about 24 hours. Conception odds are highest in the two days right before ovulation.
Example
With a period starting July 1 and a 30-day cycle: ovulation lands around July 17 (day 16), the fertile window runs about July 12–18, and the next period is expected around July 31.
When Estimates Struggle
Calendar estimates are least reliable with irregular cycles, recent hormonal birth control use, breastfeeding, or conditions like PCOS. In those cases ovulation predictor kits (which detect the LH surge) give far better timing than any calendar.
Frequently Asked Questions
When do you ovulate in a 28-day cycle?
Around day 14 — about 14 days before your next period. In longer or shorter cycles, ovulation shifts with the cycle: it's roughly your cycle length minus 14.
How many days are you fertile each cycle?
About six: the five days before ovulation plus ovulation day itself. Sperm survive up to five days, while the egg is viable for about 24 hours after release.
Can I use an ovulation calculator to avoid pregnancy?
No — calendar estimates are not reliable enough for contraception. Cycles vary month to month, and sperm survival adds more uncertainty. Use proper contraception and talk to your healthcare provider.
When should I take a pregnancy test?
The most reliable time is on or after the first day of your missed period. Testing earlier often produces false negatives because hCG hasn't risen enough yet.