Ovulation Calculator
Estimate your next ovulation date and fertile window based on your cycle.
How this calculator works
Ovulation typically occurs about 14 days before the next period starts, regardless of overall cycle length — this calculator counts forward from your last period using that logic.
The fertile window spans roughly 5 days before ovulation through 1 day after.
How reliable is this estimate?
This gives a statistical estimate based on average cycle patterns — actual ovulation timing varies month to month and person to person, so it works best alongside other tracking methods for those trying to conceive or avoid pregnancy.
Improving prediction accuracy
Calendar-based estimates like this one work best for people with regular, consistent cycles. For more precise tracking, many people combine this estimate with ovulation predictor kits (which detect a hormone surge before ovulation) or basal body temperature tracking (which confirms ovulation has occurred after the fact).
Tracking your actual cycle length over 3-6 months, rather than assuming a standard 28-day cycle, can also meaningfully improve the accuracy of calendar-based predictions like this one.
A worked example
With a last period starting June 1 and a 30-day average cycle: ovulation is estimated around June 17 (30 minus 14 equals 16 days after June 1), with a fertile window of roughly June 12-18.
For a shorter 26-day cycle starting on the same date, ovulation shifts earlier to around June 13, illustrating how cycle length directly shifts the entire fertile window even from the same start date.
Signs of ovulation beyond calendar tracking
Calendar-based estimates like this one work best combined with physical signs of ovulation — changes in cervical mucus, a slight rise in basal body temperature after ovulation, and mild pelvic discomfort some people notice can all help pinpoint timing more precisely than date-counting alone.
Ovulation predictor kits, which detect a hormone surge (LH) that occurs shortly before ovulation, are another commonly used method that can improve accuracy beyond calendar tracking, particularly for those with less predictable cycles.
Frequently asked questions
How accurate is ovulation calendar tracking?
It's a reasonable estimate for people with regular cycles, but actual ovulation can shift due to stress, illness, and other factors — tracking basal body temperature or using ovulation test kits improves accuracy.
How long is the fertile window each cycle?
Typically about 6 days — the 5 days leading up to ovulation plus the day of ovulation itself, since sperm can survive several days while the egg is viable for about 24 hours.
Can ovulation timing vary month to month?
Yes, even for people with generally regular cycles — stress, illness, travel, and other factors can shift ovulation timing from one cycle to the next.
What are ovulation predictor kits?
Over-the-counter tests that detect a rise in luteinizing hormone (LH) shortly before ovulation, generally offering more precise timing than calendar-based estimates alone.