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How to Track an Irregular Menstrual Cycle

Irregular cycles are harder to track but more important to document. What counts as irregular, how to build a useful baseline, and when to see a provider.

What Makes a Cycle "Irregular" The word irregular covers a wide range. Some people have cycles that vary by a week or more each month but have always been that way. Others experience a sudden change in cycle length or frequency that is new. Both are worth tracking, but for different reasons. A useful working definition: a cycle is irregular if it falls outside the 21 to 35 day window, if cycle length varies by more than seven to nine days between consecutive cycles, or if periods are absent for more than 90 days. Single outliers happen; a pattern of them is clinically relevant. Building a Baseline With Inconsistent Data When cycles are irregular, the instinct is to stop tracking because the data seems useless. That instinct is wrong. Irregular cycles need more tracking, not less, because the variation itself is the information. After three to six cycles, you have a range. After twelve cycles, you have a pattern that shows whether the irregularity is consistent (cycles always run 30 to 60 days), trending (cycles getting progressively longer), or sporadic (usually regular with occasional long outliers). Each of these patterns suggests different things clinically and produces differen