What is an irregular period?
An irregular period is one that falls outside the typical range or whose timing is unpredictable — cycles that are consistently longer or shorter than usual, or that vary a lot from one to the next. The NHS describes the typical range as roughly 21 to 35 days while noting everyone differs; stepping outside that, or swinging unpredictably within it, is what 'irregular' usually means.
Length and unpredictability both count
Irregularity isn't only about cycles being long. A cycle can sit within the typical range yet still be irregular if its timing jumps around — 24 days, then 33, then 27. Equally, consistently long cycles count as irregular even if they're predictable. Both matter because both are patterns a GP assesses. Infrequent periods (longer gaps) and variable timing are among the cycle features looked at when PCOS is being considered, alongside other causes.
Why the interval view reveals it
The clearest way to see irregularity is to measure the interval between period starts, cycle after cycle. Trying to predict a date assumes regularity you may not have; counting the gap instead simply records what happened. Over a few months, that interval view turns 'my periods are all over the place' into a set of actual numbers — the kind of evidence a GP can read at a glance and reason about. It also captures the spread, not just an average: knowing your cycles ran anywhere from 26 to 49 days says more about irregularity than a single typical figure ever could, and it's that spread a clinician often wants to see.
PCOS Diary measures the interval between period starts, so irregularity — long, short or variable — shows up as numbers in a doctor-ready PDF.
Common questions
- Are my periods irregular if they're long but predictable?
- They can still count as irregular. Cycles consistently outside the typical 21-to-35-day range are considered irregular even when predictable, just as variable timing within the range is. Both are patterns worth recording and raising.
- How many months of dates do I need to tell?
- A few cycles usually start to reveal whether timing is variable or lengths sit outside the typical range. The more period-start dates you have, the clearer the pattern — and the more a GP can work with.
- How do I describe irregular cycles to a GP without it sounding vague?
- Give them the spread, not an average. 'Over the last six months my cycles ran anywhere from 26 to 49 days' tells a GP both the range and the unpredictability in one line, where 'my periods are all over the place' leaves them nothing to reason about. The interval view hands you exactly those numbers, so the appointment starts from evidence rather than impression.