ToolsPeriod Calculator
Women's health & pregnancy
Period Calculator
A simple way to look ahead at your next few cycles and your fertile window, from the date your last period began.
Want to know what this means for you?Ask Seri
Part of Seri Bloom, one of Seri's health companions.
How it's calculated
We add your typical cycle length to your last start date to project upcoming periods, and place your fertile window around ovulation, roughly 14 days before your next period is due.
How to read your result
These dates assume a fairly regular cycle. Real cycles shift with stress, travel, illness and life stage, so treat the predictions as a guide. This is not a reliable way to avoid or plan pregnancy.
Common questions
Good if your cycles are regular, less so if they vary. Tracking a few real cycles makes the estimate sharper over time.
Method: Calendar method from cycle length.