I haven’t studied every online tool for period tracking but this one appears to be the most sophisticated yet: MikvahCalendar.com helps observant Jewish women track their cycles, including her niddah (ritually impure) time. It automatically calculates sunrise and sunset, sends email or text reminders, and can be customized for Chabad, Ashkenazic, and Sephardic traditions. And it’s Rabbincally Approved.
