Irregular Cycle Calculator

A single cycle length tells you very little about your cycle pattern. It is only by tracking multiple cycles and looking at how much they vary from one another that a meaningful picture emerges. This calculator takes up to six recent cycle lengths — measured from the first day of one period to the first day of the next — and returns your average cycle length, your shortest and longest recorded cycles, the total variation range, and a label indicating how regular or irregular your pattern appears based on that data. A variation of 7 days or fewer is generally considered fairly regular. Variations of 8–13 days are somewhat irregular but within a range many people experience. Variations of 14 days or more are generally considered irregular and worth discussing with a healthcare provider to explore potential underlying causes. Cycle variation is completely normal to some degree — stress, illness, travel, changes in sleep, and nutrition can all affect cycle length in a given month. What matters more is the pattern across several cycles over time, which is why tracking multiple data points gives far more useful information than any single cycle reading.

Enter the length of each recent cycle — measured from the first day of one period to the first day of the next. The calculator filters out any zero entries (used to mark optional fields as empty), then computes the average across all entered cycles, finds the shortest and longest, and subtracts to get the variation range. The regularity label is based on that variation: 7 days or fewer is fairly regular, 8–13 days is somewhat irregular, and 14 or more days is considered irregular. Tracking at least 3 cycles, and ideally 6, gives a more accurate and meaningful picture than any single cycle alone.