Fertile-window and cycle timeline estimate
Calendar estimates are most useful for regular cycles. Do not use this calculator as contraception.
Your estimated cycle
Evidence-based guide
An ovulation calculator estimates when ovulation may occur from the first day of the last menstrual period, average cycle length, and luteal-phase length. It is a planning tool for people with reasonably regular cycles, not a test that confirms ovulation.
Projects the next period from average cycle length, then counts backward by the estimated luteal phase.
Includes the five days before estimated ovulation and approximately one day afterward because sperm and egg survival overlap across this interval.
LH urine tests, cervical mucus observations, and basal body temperature can add information that a calendar estimate cannot provide.
The highlighted fertile window represents higher-probability days, not guaranteed fertile or infertile dates. Ovulation can shift between cycles even when bleeding appears regular. The implantation interval is an approximate biological range rather than a date that can be observed from calendar data.
Cycles may change with postpartum recovery, breastfeeding, perimenopause, polycystic ovary syndrome, illness, travel, stress, and hormonal medication. Calendar prediction must not be used as the sole method of contraception.
Yes. The common 14-day estimate describes an average luteal phase, and individual timing can vary.
A practical estimate is the five days before ovulation through about one day afterward.
No. Regular bleeding makes calendar prediction more useful but does not directly confirm egg release.
Seek clinical advice for persistently irregular or absent periods, significant pain, unusual bleeding, or difficulty conceiving.
