Ovulation calculator
Estimate your fertile days without creating an account or sharing your dates.
Direct answer: for a predictable cycle, ovulation is often estimated about 14 days before the next period. The fertile window spans roughly the five days before ovulation through one day afterward.
Calendar estimates are less reliable with irregular cycles and cannot confirm ovulation. Body signs or clinical testing may tell a different story.
A useful estimate, not a test
This calculator counts back from the next expected period using a typical luteal phase. That makes it a practical planning aid for predictable cycles, but real ovulation can move because of stress, illness, travel and normal variation.
ACOG's fertility-window guidance describes a window of about six days and explains that there is no foolproof way to calculate fertile days. If your cycles vary, use the result as a wider planning window rather than a single target date.
Common questions
When is the fertile window?
ACOG describes a roughly six-day fertile window: up to five days before ovulation through about one day afterward.
Can a calculator confirm ovulation?
No. It estimates timing from cycle dates. Ovulation tests, cervical mucus, basal temperature patterns or clinical care may provide more information.
Does this work for irregular periods?
It is less reliable when cycle length varies. ACOG notes that predicting ovulation at home may not be useful for highly irregular periods.