In short
If your cycle has dropped from its usual length to 24 or 25 days, that shift is often the very first sign of early perimenopause. It happens because ovulation is arriving earlier and progesterone is falling, says Sarah McLachlan, The Perimenopause Naturopath (BHSc Naturopathy). It's not something you've done wrong, and there's plenty you can do to feel better.
In this post:
- What a normal cycle length actually is
- Why cycles shorten in your 40s (and why they often get heavier too)
- How doctors define the start of the menopause transition
- What helps, and when to see your GP
Noticed your period arriving more often since you hit your 40s? You're not imagining it, and it's happening for a reason. Here's what's going on, and what you can do about it.
What is a normal menstrual cycle length?
A normal menstrual cycle falls between 24 and 38 days, by the international (FIGO) definition. Within a year, your cycle length can vary by up to 9 days and still count as "normal". In my experience, most women sit between 26 and 30 days, and the number that matters most is YOUR usual number. If you've run like clockwork at 30 days for two decades and you're suddenly seeing 24s and 25s, that change is worth paying attention to, even though both numbers are technically "normal".
Why are my cycles suddenly shorter?
Because ovulation is arriving earlier. In your 40s, your ovaries need more stimulation to mature an egg, so the brain raises FSH, the follicle races to the finish line sooner, and the first half of your cycle (the follicular phase) shrinks. The result: a cycle that used to be 29 days arrives at 24 or 25.
Cycles of 21 to 26 days are a hallmark of early perimenopause, and they rarely travel alone: more PMS, sore breasts, mood changes, brain fog and disturbed sleep often arrive with them. The formal staging system doctors use (STRAW+10) says the menopause transition has begun when your cycle length persistently differs by 7 or more days from what it used to be (Harlow et al., 2012).
Why are shorter cycles often heavier too?
Because progesterone is falling faster than oestrogen. Progesterone is made after ovulation, and as ovulation becomes patchier (including cycles where you don't ovulate at all), there's less of it to keep the uterine lining in check. Oestrogen, meanwhile, is swinging high and low rather than declining smoothly, and the high swings build a thicker lining. Thicker lining + more frequent periods = heavier, often more painful, bleeding, more frequently.
A 2025 study of over 2,300 midlife women found up to 1 in 3 experienced heavy or prolonged bleeding during the menopause transition, and that this bleeding was strongly linked to fatigue (Harlow et al., Menopause, 2025). More bleeding days per year also quietly drains your iron stores, which is why shorter cycles and exhaustion so often arrive together.
Shorter cycles in your 40s
The shrinking cycle
When cycles drop from 28 days to 24, the same three months fit an extra period.
Your 30s: cycles about 28 days
Three periods across twelve weeks.
Your 40s: cycles about 24 days
Ovulation arrives earlier, so periods arrive closer together.
the extra period
More PMS days per year
More bleeding days per year
More iron quietly lost
It's not you. It's ovulation
arriving earlier.
Cycles of 21 to 26 days are a hallmark of early perimenopause.
Can anything be done about shorter cycles?
Yes and no. Shorter cycles are part of how your body winds down its reproductive years, and no supplement stops that process. But in my opinion, that was never the real goal. The real goal is to smooth the oestrogen rollercoaster and support the progesterone you still make, so the symptoms that ride along with shorter cycles (PMS, sore breasts, mood swings, heavy bleeding, poor sleep) ease off.
I also encourage women to hold onto their cycles rather than wishing them gone: while your ovaries are still cycling, you're still getting oestrogen's protective benefits for your bones, heart and brain.
What helps:
- Know your pattern. Track your cycle length for a few months so you have real numbers, not vibes. That record is gold for you, your GP and your naturopath.
- Support progesterone production with the basics it depends on: managing stress (cortisol competes directly with progesterone), enough protein and healthy fats, and not over-restricting food. My blog on low progesterone covers this properly.
- Look after your iron if your periods are heavier or more frequent. Shorter cycles mean more bleeding days per year, and iron quietly drains away. Here's how to spot and fix iron deficiency in perimenopause.
- Address heavy bleeding rather than enduring it. Heavy bleeding in perimenopause is common, but common doesn't equal normal, and it's treatable.
- Understand where you are in the transition. The stages make far more sense when you can see the map: the phases of perimenopause.
When should you see your GP about your cycles?
- Your cycles are persistently shorter than 21 days
- You're bleeding between periods or after sex
- You're soaking through a pad or tampon every hour, passing large clots, or bleeding for more than 8 days
- Any bleeding after 12 months without a period
- You feel breathless, dizzy or exhausted with heavy bleeding (get your iron checked)
These need a medical assessment first; naturopathic support works alongside, not instead.
You're not imagining it
If your cycle has changed and you feel like your body has swapped the rules without telling you, that's exactly what early perimenopause feels like, and you don't have to white-knuckle through it. Book a free Clarity Call and we'll look at your pattern, your symptoms and your options together.
Frequently asked questions
Why is my cycle getting shorter in my 40s?
Because ovulation is happening earlier in your cycle. In your 40s the brain raises FSH to stimulate ageing ovaries, the egg matures faster, and the first half of your cycle shortens. A cycle dropping from 28 to 30 days down to 24 to 26 days is often the very first sign of early perimenopause.
Is a 21-day cycle normal in your 40s?
It's common in early perimenopause, but it sits at the very bottom of the normal range (24 to 38 days by the FIGO definition). Cycles persistently shorter than 21 days deserve a GP check to rule out other causes, and cycles of 21 to 26 days with heavier bleeding are a classic early perimenopause pattern worth supporting properly.
Do shorter cycles mean menopause is close?
Not necessarily. Shorter cycles mark the EARLY part of the transition, which can last years. Closer to menopause, the pattern usually flips: cycles space out, you skip periods, and gaps of 60 days or more appear. Shorter cycles are the entry ramp, not the exit.
Why are my periods heavier as well as closer together?
Falling progesterone and swinging oestrogen. With patchier ovulation there's less progesterone to keep the uterine lining in check, while oestrogen's high swings build a thicker lining. The result is heavier, often more painful periods arriving more often. Heavy bleeding is treatable, so please don't just endure it.
Can you make your cycle longer again?
No supplement reliably lengthens a shortening perimenopausal cycle, and anyone promising that is overreaching. What you can do is support the hormones you still make, so the symptoms riding along with shorter cycles ease: steadier moods, less PMS, lighter bleeding and better sleep are realistic goals.
Do shorter cycles cause low iron?
They contribute, yes. More periods per year means more bleeding days per year, and if those periods are also heavier, iron drains faster than food alone can replace it. If you're exhausted, foggy or losing hair alongside shorter cycles, ask for iron studies including ferritin.
References
- Munro MG, et al. The FIGO classification systems for normal cycle parameters and abnormal uterine bleeding. pubmed.ncbi.nlm.nih.gov
- Harlow SD, et al. Executive summary of the Stages of Reproductive Aging Workshop + 10. Journal of Clinical Endocrinology and Metabolism. 2012;97(4). doi.org
- Harlow SD, et al. Abnormal uterine bleeding is associated with fatigue during the menopause transition. Menopause. 2025. pubmed.ncbi.nlm.nih.gov
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