Calculator Fertility
Ovulation calculator
Ovulation usually happens about 14 days before your next period. Enter your last period and cycle length to estimate your fertile window — the roughly six days when conception is possible.
Your estimated fertile window
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By the numbers Context
When you ovulate and how the fertile window works
In a typical cycle, one egg is released about 14 days before the next period begins. That is the key to timing: because cycle length varies from person to person, ovulation is best counted backward from the next expected period rather than forward from the last one. This calculator estimates it from your cycle length and, if you know it, your luteal-phase length.
Conception is possible across roughly six days each cycle — the five days leading up to ovulation plus ovulation day itself. That window exists because sperm can survive up to about five days in the reproductive tract, while a released egg is only viable for around 12 to 24 hours. Real ovulation shifts month to month, so for trying to conceive, ovulation predictor kits or tracking your basal body temperature can pinpoint it more precisely than the calendar alone.
6 days
the fertile window each cycle (5 days before + ovulation day)
Research
~14 days
before your next period is when ovulation typically occurs
Clinical
12–24 hrs
how long an egg stays viable after it is released
Clinical
Sources: standard reproductive-health references; Wilcox et al. on the fertile window.
Frequently asked questions
When do I ovulate?
Ovulation typically happens about 14 days before your next period. In a 28-day cycle that is around day 14, but in a 30-day cycle it is closer to day 16. This calculator estimates your date from your own cycle length.
What are the most fertile days?
The two to three days leading up to and including ovulation are the most fertile. The full fertile window is about six days — the five days before ovulation plus ovulation day.
How many days after my period do I ovulate?
It depends on your cycle length, not a fixed number of days after your period. Counting backward is more reliable: ovulation is about 14 days before your next period starts.
Can I get pregnant right after my period?
It is less likely but possible, especially with short cycles, because sperm can survive several days and may still be present when you ovulate. The calculator shows your specific fertile window.
How accurate is an ovulation calculator?
It gives a good estimate based on average timing, but real ovulation shifts from cycle to cycle. Ovulation predictor kits or basal body temperature tracking are more precise if you are actively trying to conceive.