Period & Cycle Calculator

How the calculator works

Your cycle is counted from the first day of one period to the first day of the next. We take the date you entered and your cycle length to estimate your next period (that date plus your cycle length), which phase you're in today, and an ovulation window — since the luteal phase is biologically about 14 days, we place ovulation roughly 14 days before your next expected period, and show the days around it when conception is most likely.

The four phases, briefly

• Menstrual — your period; hormones are low and rest often feels welcome.
• Follicular — after your period; estrogen rises and energy often returns.
• Ovulation — mid-cycle; an egg is released, your most fertile window.
• Luteal & PMS — the winding-down stretch before your next period.

Want the plain-language version? Read what your hormones do in each phase, or explore the full Cycle Library.

Looking for something more specific? Work out when your next period is due, find how long your cycle actually is, see which phase your birthday or anniversary lands in with the Anniversary Almanac, or see why this is a period tracker with no account.