Menstrual Cycle Calculator
Use your cycle length or four recent period start dates to see a single-cycle calendar.
Open calculator →Your cycle, made simpler
Understand your menstrual cycle with clarity.
Explore estimated period dates, ovulation timing and a possible fertile window. Calculations stay in your browser.
Use free cycle calculator →Educational estimates only. No calendar day is guaranteed safe for avoiding pregnancy.
Explore MyCycle Guide
Period & Ovulation Guides
Plain-language articles with medical source references and clear limitations.
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Featured guides
Menstrual Cycle Basics
What counts as Day 1 and why cycles vary.
Ovulation & the Fertile Window
What a calendar can and cannot estimate.
Are There Safe Days?
Understand why no calendar date guarantees zero pregnancy risk.