Fertile-window estimate
See a likely ovulation day and six-day fertile window based on your recent cycle average. It is a useful orientation, never a contraception method.
Your dates stay on this device. Nothing you enter here is saved or sent to Flowy.
The calculation
The estimate assumes ovulation may happen about 14 days before the next period. We first add your average cycle length to the latest period start, then count back 14 days.
The fertile-window estimate begins five days before the ovulation estimate and ends on that day, creating the roughly six-day window described by the Office on Women’s Health.
Good to know
Ovulation is a biological event, not a fixed calendar appointment. Illness, stress, postpartum changes, perimenopause, PCOS, and other factors can shift or interrupt it.
This result cannot confirm ovulation and must not be used to avoid pregnancy. If you are trying to conceive and have questions about timing or fertility, a healthcare professional can offer individualized guidance.
Common questions
It estimates the next period from your average cycle length, then counts back about 14 days for likely ovulation. The displayed fertile window covers the five days before that estimate and the estimated ovulation day.
There are about six days in a cycle when pregnancy is possible, but the calendar dates vary because ovulation can shift. This tool estimates those dates; it cannot confirm ovulation.
No. Calendar estimates are not reliable contraception and cannot identify every potentially fertile day. Discuss contraceptive options with a qualified healthcare professional.
Yes. A single average hides variation, so the result is less useful when cycle lengths change. Ovulation may also shift even when periods usually look regular.
