Menstrual Cycle Calculator

Reviewed by the CalculatorHub team, edited by James Graham. Method from Office on Womens Health: Your menstrual cycle. Last verified 2026-06-23.

The Menstrual Cycle Calculator computes menstrual cycle from the relation estimated ovulation day = cycle length - luteal phase length. It takes 2 inputs (average cycle length in days, luteal phase length in days) and returns the menstrual cycle. These calculators are for anyone tracking a cycle, a pregnancy or a new baby, and for the midwives, nurses and doctors supporting them, turning recorded dates and measurements into the timing and growth figures used to anticipate what comes next, follow progress against expected patterns, and decide what to raise at the next appointment. Enter your values below and the result updates instantly, and you can share a permalink that pre-fills the exact calculation. These outputs follow directly from the dates and measurements you enter, so use dates exactly as recorded rather than rounded recollections, keep weight and length figures in one unit system where a tool asks for them, and read any single result as less telling than the pattern that builds up over repeated cycles or measurements. For example, with average cycle length = 30 days, luteal phase length = 14 days, the menstrual cycle works out to 16, and the worked example further down the page shows every step so you can follow the arithmetic and reproduce it by hand. The method is the standard form documented by Office on Womens Health: Your menstrual cycle, and the figure above each result carries the date it was last verified. Cycles, pregnancies and babies all vary widely, and these figures describe typical ranges rather than an assessment of any individual, so discuss anything that worries you, or any result that falls outside what you expected, with your midwife, doctor or pediatrician.