A Menstrual-Tracking App Debunked the Myth of the 28-Day Cycle

Let’s quit comparing ourselves to the myth of ‘normal’

Darcy Reeder
Mar 6, 2020 · 6 min read

My period hasn’t arrived. But what else is new? Every single cycle, I’m late. And I’m doing that thing I do — that thing most of us do— I’m getting mad at my body, how unpredictable it is, how .

As I turn to Google again — and wonder if everyone’s phone autofills “for a missed period” when they type the word “reasons,” or is that just me?— I learn something new. Something ancient, actually, but new to me.

Myth: The average menstrual cycle is 28 days.

We’ve all been told a million times 28 days is normal and average. First off, even if that were true, averages are just averages, and we deserve to love ourselves and our bodies in all their beautiful variability. But the truth is, the average is probably more like 29.3 days. Wait, what?

The 29.3 days figure comes from crowdsourced data from over 600,000 menstrual cycles anonymously collected from 124,648 users of the menstrual-tracking app Natural Cycles. A study, funded by the company that made the app, was published in 2019 in the journal npj Digital Medicine. Researchers excluded data from users with a polycystic ovarian syndrome diagnosis, signs of menopause, or anyone who used hormonal contraception in the year leading up to their start on the app.

There’s power in knowing the standard was a lie, that even if we’ve gotten the message our whole lives that something is wrong or weird about us, it doesn’t make it true.

Only 13% of the cycles in the study were 28 days long, though that hasn’t stopped major health information sources from continuing to quote 28 days as “average” and “normal.” For example, the US Office on Women’s Health, the UK’s National Health Service, WebMD, Health.com, MedicineNet, and Cleveland Clinic all continue to parrot the old line that 28 days is average. Even when their well-intentioned point is most of us don’t fit the average, they repeat the 28 days figure.

Shoutout to the Mayo Clinic for being an outlier and defining this way: “The menstrual cycle, which is counted from the first day of one period to the first day of the next, isn’t the same for every woman. Menstrual flow might occur every 21 to 35 days and last two to seven days…. Within a broad range, ‘normal’ is what’s normal for you.”

Myth: Ovulation usually occurs on Day 14 of your cycle.

Okay, we really have to demystify this, because predicting ovulation is central both to trying to conceive and trying not to conceive. (Predicting our periods is more a matter of whether or not we stain another nice pair of undies.)

The Natural Cycles app study found huge variability in when ovulation occurred, which fits with the American Pregnancy Association’s guidance: “Most women ovulate anywhere between Day 11-Day 21 of their cycle, counting from the first day of their last period… Ovulation can occur at any point during this window and may occur on a different day each month.”

When I charted my ovulation while trying to conceive, most helpful was learning to observe my own cervical mucus. Personally, it was a reliable indicator of when I was ovulating and gave me a new confidence in my body (that I should probably revisit). Here’s Planned Parenthood telling us everything we ever wanted to know about cervical mucus, as it pertains to ovulation.

Myth: The moon’s cycle is 28 days.

Okay, wait, what? They even lied to us about the moon!?

When I learned menstrual cycles don’t average out at 28 days, I thought that meant I could no longer dream about being a magical moon-witch. But it turns out the moon’s cycle isn’t 28 days either. It’s actually 29.5 days, which is eerily similar to the 29.3-day average menstrual cycle in the Natural Cycles app’s crowdsourced data!

It’s possible we just told ourselves the moon cycles were 28 days so we could keep believing the moon matched up with our menstrual cycles. But now that we’ve destroyed the myth that our own cycles are usually 28 days, we can pay attention to the moon’s well-charted reality. The time from one new moon to the next new moon is definitely 29.5 days, not 28.

So go ahead, witches, if you want to picture your feminine power flowing with the moon and the tides, go for it.

Wait, but oral contraception comes with 28 pills.

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Photo by Thought Catalog on Unsplash

Yeah, it does. A pill pack has 28 pills for a 28-day cycle: You take three weeks of hormones, then one week of placebos. Some birth control pills — like the progestin-only “mini-pill” — have no placebos but still come in 28-day packs.

And maybe that’s why I made it to the ripe old age of 36 still believing my menstrual cycle was 28 days long. For many, many years, my cycle exactly 28 days, but only because the hormones in my birth control pills made it that way.

With oral contraception, remembering to take your pill every day is key. So there are routine-based benefits to having a constant day of the week to start a new pack or row. But that doesn’t mean it’s more normal or natural or even average for your cycle to be divisible by 7.

That’s why the Natural Cycles app study excluded data from anyone who used hormonal birth control in the year leading up to getting the app: Hormonal birth control shapes our cycles rather than maintaining them.

Now that I’m no longer using any birth control — aside from monogamy and my partner’s vasectomy — I am not beholden to the enforced cycle of the pill. And 28 days — or 29.3 for that matter — is not what my body wants to do right now.

“Menstrual flow might occur every 21 to 35 days…. Within a broad range, ‘normal’ is what’s normal for you.” — the Mayo Clinic

Don’t get me wrong, I’m very thankful for the pill and all the other birth control options we have (as well as the availability of safe, legal abortion).

But I’m learning about body now, cycle. That cycle might get as predictable as the moon, or it might fumble around until my eventual, long trek through menopause.

There’s power in knowing the standard was a lie. Even if we’ve gotten the message our whole lives that something is wrong or weird about us, it doesn’t make it true.

Myth: Our bodies are all fucked up.

Sometimes I think what unites us most is our shared experience of body shame. Our entire lives, our cultures have told us we’re too fat or flat or short or tall or dark or freckly or hairy or bumpy or smelly. We grow up taking for granted that our bodies are sabotaging us, that we must control them, beat them into submission.

and i said to my body. softly. ‘i want to be your friend.’ it took a long breath. and replied ‘i have been waiting my whole life for this.’ —poet Nayyirah Waheed

What if you could acknowledge you are not a work-in-progress? You are you, right now, right here. And it doesn’t matter if you’re, because there is no normal.

When you let yourself accept your body as it is, when you listen to your body, you’re more likely to notice if something’s truly wrong. If there’s a big change in your body, then without shame, you can get curious, and get help if you need it.

As for me, nothing’s wrong. I am not broken. My cycles don’t fit into a 4x7 grid. But then again, neither does the moon’s.

Fearless She Wrote

This is a space to empower differences, tell our stories…

Darcy Reeder

Written by

Empathy for the win! Published in Gen, Human Parts, Heated, Tenderly —Feminism, Sexuality, Veganism, Anti-Racism, Parenting. She/They darcyreeder.substack.com

Fearless She Wrote

This is a space to empower differences, tell our stories, and share our lives together. We will not be silenced. We will be fearless. And we will write.

Darcy Reeder

Written by

Empathy for the win! Published in Gen, Human Parts, Heated, Tenderly —Feminism, Sexuality, Veganism, Anti-Racism, Parenting. She/They darcyreeder.substack.com

Fearless She Wrote

This is a space to empower differences, tell our stories, and share our lives together. We will not be silenced. We will be fearless. And we will write.

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