Why is my period irregular?
Periods are usually irregular because ovulation isn't happening on a steady schedule. Common reasons include the first years after periods start, stress, big weight changes, intense exercise, coming off hormonal contraception, breastfeeding, PCOS, thyroid problems and perimenopause. Irregular means cycle lengths vary by more than about 7 to 9 days, or often fall outside 21 to 35 days.
What counts as irregular?
Nobody's cycle is identical every month. Small changes are normal. Doctors usually call periods irregular when:
- the gap between your shortest and longest cycle is more than about 7 to 9 days
- cycles are often shorter than 21 days or longer than 35 days
- you skip periods, or go three months or more without one
- you bleed between periods
Common causes of irregular periods
| Cause | Typical clues |
|---|---|
| Recently started periods | First 2 to 3 years; cycles up to 45 days are common |
| Stress, illness, travel | One or two cycles thrown off, then back to normal |
| Weight loss, under-eating, intense exercise | Long or missing cycles |
| Hormonal contraception (starting or stopping) | Spotting, unpredictable bleeding for a few months |
| Breastfeeding | Periods absent or irregular until weaning |
| PCOS | Long cycles, acne, extra hair, weight gain |
| Thyroid problems | Tiredness, weight change, feeling cold or hot |
| High prolactin | Milky nipple discharge, headaches |
| Perimenopause | 40s; shorter, then longer or skipped cycles |
| Fibroids, polyps, endometriosis | Heavy or painful periods, bleeding between periods |
Learn more on irregular periods, PCOS and coming off the pill.
Irregular periods and mood
When cycles are unpredictable, PMS is unpredictable too. Low or irritable days can seem to come out of nowhere, which is harder than the symptoms themselves. Tracking mood alongside bleeding helps you link the two, even when the calendar can't.
What to do
- Rule out pregnancy if a period is late and pregnancy is possible.
- Log every period start and any spotting for three or more months.
- Note what else is going on: stress, weight change, new exercise, new medicines.
- Bring your log to a doctor if the pattern continues. It makes diagnosis much faster.
Lulu doesn't assume 28 days. It learns from your own cycles and widens its estimates when your cycles vary, rather than pretending to be precise. See tracking irregular cycles.
When to see a doctor
See a doctor if your periods have been irregular for several months, if you go three months without a period, if cycles are often under 21 or over 35 days, if you bleed between periods or after sex, or if irregular periods come with acne, hair growth, weight change, very heavy bleeding or severe pain.
Frequently asked questions
Can irregular periods be normal?
Yes, in the first few years after periods start, after childbirth, while breastfeeding and in perimenopause. Outside those times, a lasting change is worth checking.
Can you get pregnant with irregular periods?
Yes, as long as you ovulate. It's harder to predict when, so use contraception if you don't want to get pregnant.
Do period apps work with irregular cycles?
They can, if they learn from your history rather than assuming 28 days. See do period apps work for irregular cycles.
Why do I get two periods in one month?
Short cycles or bleeding between periods can cause it. See two periods in one month.
Sources
- NHS: Irregular periods
- NICHD: What causes menstrual irregularities?
- Cleveland Clinic: Abnormal menstruation
- ACOG: Abnormal Uterine Bleeding
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.
PCOS (now also called PMOS) and your cyclePCOS, now also called PMOS, explained: the common signs, how doctors diagnose it, what it does to your cycle and mood, and what helps day to day.How to track irregular periods (and make sense of them)How to track irregular periods: what counts as irregular, what to log, how to read your range instead of an average, and when irregular cycles need 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.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.