Irregular periods in your 40s: what's typical and when to check

For most women, the first sign of perimenopause is the cycle. Periods that arrived dependably for two decades start to drift — by a few days at first, sometimes by weeks, sometimes skipping a month altogether before coming back like nothing happened.

This is normal. It’s also worth understanding which patterns are typical and which deserve a clinician’s attention.

What’s typical

The Stages of Reproductive Aging Workshop (STRAW) framework — the international standard for staging the menopause transition — defines early perimenopause as the point when cycle length varies by 7 or more days from your personal baseline, in 2 or more cycles out of 10 consecutive ones.

Common typical patterns include:

• Shorter cycles — particularly in the early phase, as the follicular stage shortens
• Longer cycles — common as ovulation becomes more erratic
• Skipped periods — months of amenorrhea followed by a return of menses (especially in late perimenopause)
• Heavier or lighter flow — within reason; many women cycle between extremes
• Spotting before a period — common with anovulatory cycles

Late perimenopause is defined as a 60-day or longer gap between periods. Menopause itself is defined retrospectively: 12 consecutive months without a period.

What’s not typical

Some bleeding patterns are not typical perimenopause and need a clinician visit:

• Soaking through a pad or tampon every hour for 2+ hours. Acute heavy menstrual bleeding can cause anemia and sometimes signals a treatable structural cause (fibroids, polyps, hyperplasia).
• Bleeding between periods that’s new and persistent. Should be evaluated for endometrial pathology.
• Bleeding after sex. Can suggest cervical pathology.
• Bleeding 12+ months after your last period. Postmenopausal bleeding is endometrial cancer until proven otherwise — almost always nothing serious, but always worth checking.
• Periods so heavy you’re rearranging your life around them. Even if individually each period is “manageable,” a quality-of-life burden is itself a reason to seek care.

If you’re experiencing any of these, our when to see a doctor guide breaks down urgency tiers.

Why it changes

The ovaries don’t run out of eggs all at once. Through the late 30s and 40s, the rate of follicle decline accelerates. Each cycle becomes more variable — sometimes ovulation happens, sometimes it doesn’t. When ovulation doesn’t happen, progesterone isn’t made, and the lining of the uterus can build up unevenly. That’s why anovulatory cycles often produce both lighter and heavier bleeds in different months.

Confounders to keep in mind

Cycle changes don’t always mean perimenopause. Other common causes in this age window:

• Pregnancy. Worth ruling out before assuming perimenopause; perimenopause is not contraception.
• Thyroid disease (especially hypothyroidism, which can cause heavier periods).
• Polyps or fibroids.
• Coagulation disorders (sometimes diagnosed later in life).
• Significant weight change in either direction.
• Strenuous exercise increases.

What helps

For most women, irregular periods don’t require treatment — just understanding. Practical steps:

1. Track them. A simple app or paper log helps you see pattern. Note start date, duration, and a flow estimate (light / medium / heavy / soaking).
2. Have a stash of supplies. Period underwear, menstrual cups, or a backup pack means an unexpected start doesn’t derail your day.
3. Talk to your clinician if any of the “not typical” patterns appear, or if quality of life is taking a hit.

When to take the symptom check

If irregular periods are showing up alongside other changes (sleep, mood, hot flashes, energy), our 3-minute symptom check helps you see the bigger picture before an appointment.

The bigger picture

Cycle changes are the marker of a transition, not a problem to fix. Most variation is normal. The handful of patterns that aren’t normal are well-characterized and worth knowing — once you’ve checked those, you can let the rest just be the body recalibrating.