Ovulation and the fertile window on the calendar
What period, ovulation and fertile markers mean, and what to watch when cycle length varies.
Ovulation is the most likely day of egg release; the fertile window covers nearby days with a higher chance of pregnancy.
Period days are marked separately for orientation — that is not the same as medical advice about intercourse.
If your cycles vary a lot, a fixed-length estimate is less accurate; ovulation tests or basal temperature can help.
People trying to conceive may focus on fertile days; for contraception, do not rely on “safe days” alone.