How to track irregular periods (and make sense of them)
To track irregular periods, log the first day of every bleed, how heavy it is and how long it lasts, then look at your range rather than an average: your shortest and longest cycles. Add signs of ovulation and how you feel. After three to six months you'll know your real window, and whether the pattern is worth showing a doctor.
What counts as irregular?
Regular doesn't mean identical. Adult cycles commonly vary by a few days, and doctors usually call cycles irregular when the difference between your shortest and longest cycle is more than 7 to 9 days, or when cycles are often shorter than 21 days or longer than 35. For teens, cycles of 21 to 45 days are normal, and it can take up to six years for them to settle.
| Pattern | Usually called | Common reasons |
|---|---|---|
| Cycles 24 to 31 days | Regular | Normal variation |
| Cycles 22 to 40 days | Irregular | Stress, PCOS, perimenopause, after the pill, teens |
| Often under 21 days | Short, frequent | Perimenopause, thyroid, early ovulation; worth a check |
| Often over 35 days, or months between | Infrequent | PCOS, under-eating, intense exercise, breastfeeding, thyroid, high prolactin |
What to track
- First day of every bleed. This is the one thing that matters most. Day 1 is the first day of real flow, not spotting.
- How long it lasts and how heavy it is. Light, medium or heavy, and how often you change products on the heaviest day.
- Spotting. Note it separately; it's not day 1.
- Signs of ovulation, if you want them: egg-white discharge, a positive LH test, a temperature rise, a one-sided twinge.
- Mood and energy, once a day. Even when dates move, many people find their PMS days still come in the stretch before bleeding.
- Big events. Illness, travel, a stressful month, a new medicine or a change in training or eating.
If your last six cycles were 26, 34, 29, 38, 27 and 31 days, your average is 31, but your real window is 26 to 38. Expect your period anywhere in that window, with the most likely days near the middle.
Reading your pattern
- Find your range with the cycle length calculator: your shortest and longest cycle.
- Look for one-offs. A single long cycle after a stressful month or illness is very different from cycles that are always unpredictable.
- Check whether the luteal phase holds. If you see an ovulation sign and your period follows about 12 to 14 days later, the irregularity is in the first half of your cycle, which is the usual story.
- Watch for drift. Cycles slowly getting shorter in your 40s suggest early perimenopause. Cycles getting longer and further apart in your 20s or 30s can point toward PCOS or other hormonal causes.
- Look at your mood. If you see your harder days clustering before bleeding, you can use that as an early sign your period is coming, even when the date is uncertain.
Common causes of irregular cycles
Nearly all cycle irregularity comes from ovulation moving or not happening. Things that commonly affect it include stress, illness, travel, big changes in weight, under-eating or intense training, breastfeeding, the first months after stopping hormonal contraception, PCOS, thyroid problems, high prolactin and perimenopause. Pregnancy is the first thing to rule out if a period is late and you've had sex.
Irregular cycles and mood
Uncertainty is tiring. Not knowing whether your period will come next week or next month makes it harder to plan, and PMS can catch you off guard. Tracking mood alongside bleeding often helps more than tracking dates alone, because your body may give you a reliable warning even when the calendar can't. See mood by cycle phase.
Lulu predicts from the cycles you've logged, not a textbook 28 days, and learns how you usually feel in the days before your period, so you can get a heads-up even when the date is uncertain.
When to see a doctor
See a doctor if your cycles are regularly under 21 or over 35 days, vary by more than 7 to 9 days for several months, if you go 3 months without a period, if irregular periods come with acne, excess hair growth, weight changes or milky nipple discharge, if bleeding is very heavy or lasts over 7 days, or if you bleed between periods or after sex.
Frequently asked questions
How do you predict an irregular period?
Use your range: expect it between your shortest and longest recent cycle. Signs like breast tenderness, bloating or PMS mood changes can narrow it down.
Do period apps work with irregular cycles?
As logs, yes. Predictions are less precise, so look for one that uses your own history and shows a window. See do period apps work with irregular cycles.
Is it normal for periods to be irregular sometimes?
Yes. A one-off long or short cycle is common after stress, illness or travel.
Why is my period irregular all of a sudden?
Common reasons include stress, weight change, exercise, stopping contraception, and in your 40s, perimenopause. More in why is my period irregular.
Sources
- NHS: Irregular periods
- ACOG: Abnormal Uterine Bleeding FAQ
- ACOG: Your First Period
- Bull JR et al. Real-world menstrual cycle characteristics of more than 600,000 menstrual cycles. npj Digital Medicine (2019)
This page is for information only and isn鈥檛 medical advice. If something worries you, please talk to a doctor.
Keep reading
Irregular periods: what counts, common causes and what helpsIrregular periods explained: what counts as irregular, why cycles vary, common causes like PCOS, thyroid and perimenopause, and when to see a doctor.
Cycle length calculator: is my cycle normal?Free cycle length calculator: enter the start dates of your last few periods to get your average cycle length and see whether your cycle counts as regular.PCOS period tracker: how to track a cycle that won't follow the rulesHow to use a PCOS period tracker when cycles are long or unpredictable: what to log, why ovulation tests can mislead, and the patterns your doctor needs.Period trackers for irregular periods: what works and what to expectNeed a period tracker for irregular periods? How apps handle unpredictable cycles, which use temperature or symptoms, and what to expect from predictions.Why is my period irregular?Why is my period irregular? Stress, weight change, PCOS, thyroid issues, contraception, age and perimenopause. What counts as irregular and when to get help.