Don’t tell me girls can’t do math. Our fertile years are an endless cycle of arithmetic problems.

Welcome to Time of the Month, a Mic essay series that looks at how people who get periods consciously — or subconsciously — mark the passage of time, not by days, but by when Aunt Flo arrives for a visit. This is the first in our series: Read our second, about periods and break-ups, here; our third, about coping with how a mistimed period will ruin plans, here; and our fourth, about how many periods you can have with a guy before it’s time for The Talk, here.

The average woman starts menstruating at 12; by 51, she is menopausal. In those intervening 39 years, that average woman will have her period 450 times for an average of five days each (within an average menstrual cycle of 28 days). That means that our average chick will spend an average of 2,250 days — or just over six years in total — bleeding into a tampon, a pad, a cup or a pair of underpants. Menstruation costs this median maid money; it causes her pain; and, if our hypothetical human is anything like actual me, it makes her anxious.

Once upon a bloody time, I did lot of counting. Menstrual math, I found, both increased my anxiety and helped to calm it.

For the decades before computers, I relied on paper calendars to perform my reckoning. My cycle averaged 32 days, so I’d stab my finger on each calendar square beginning with my last period and count forward. Then I’d cross-reference the current date with my physical and emotional status. Did I detect that unholy marriage of frisky, angry, hungry and feral? Did I feel as if warring weasels had made my belly their home? Did I simultaneously want to fuck a guy and eat his liver? If so, then I knew that my body was in sync with my math: Soon my menses would arrive, and all would be well with the world.

If, however, my arithmetic and my feeling were at odds, I’d do another calculation. Were my breasts tender? How tender? Were they bigger? How much bigger? Did I feel like throwing up? How much? When? Could I be, a small voice would whisper in my head, pregnant? As days passed, I would repeat the date of my impending period in my head like a mantra, as though just repeating it would make the bleeding start.

This magical thinking was a monthly event almost every month that I had sex, which reliably happened almost every month after my 16th birthday. 

My shiniest days were the three after my period ended — the days when I knew I wasn’t pregnant. The second best set of days were the ones of actual bleeding — when I wasn’t pregnant but was messy. Every other day, when I might become or might already be pregnant, sucked equally. Thus, I had a week of good days every month, followed by three weeks of escalating fear. This, I suspect, is not an average woman’s experience.

But then, I was never average, not in one respect: I was incredibly fertile.

Of course, I used contraception of various and sundry forms: the pill, condoms, a diaphragm, those ’90s contraceptive film things that burbled and stung, the sponges of Seinfeld fame, rhythm, implants, the pullout method and murmured prayer to a baseless god. I had a hard time taking the pill because it ramped up my mildly unbalanced PMS emotional state into rampaging, irrational territory. Doctors had told me that I couldn’t use an intrauterine device because I’d had pelvic inflammatory disease. In any case, I was lepine in my fecundity; I got pregnant like other women got brunch. I could have repopulated a small village.

I did not want to be pregnant, and I didn’t want to have a baby, but my body seemed to disagree. But I dealt with the hand I got as best I could through the 1980s and 1990s, my peak fertility years, and that meant coping with the mounting anxiety every month when “Dear god, oh god, please let me not be pregnant. Dear god, please god, don’t let me be pregnant,” I thought my period was due. I bought pregnancy tests in multiples and stashed them under my sink. When I needed to assuage my anxiety, I’d pee on a stick. Most often — but not often enough — it was negative.

When online period trackers became a thing, I signed up, hoping that I could outsource my incessant menstrual math, if not my anxiety. My first was something called Monthly Info, which I started using around 2006. It reliably sent me a happy pink email a couple of days before my period arrived until — as if the site was becoming sentient to my slow slog into menopause — it didn’t. Monthly Info lost my log-in information, and years of beloved period data along with it.

By then, I had an iPhone and iPhones had period apps, so I got one. It had a flower as an icon. I used it first to count the days until I got my period, and then, as my periods became increasingly rare, I used it to count the months I didn’t.

Menopause is like a less cool version of puberty: It takes longer, your body gets less interesting, and instead of tits and pubic hair, you grow a patina of serenity. Fittingly, during my trek into menopause, I radiated with a mirror-like halo of my menstrual anxiety. Tracking my period-free months like my celebratory post-period days, I stacked them one upon another until finally, at 53, I had 12 in a row. I was officially menopausal. I exhaled with relief.

My last period was July 2015, my period app tells me — not that I’m counting, not anymore. Statistically speaking, as a healthy, college-educated, almost-married 54-year-old woman, I’ve got another 35 years ahead of me, which means I’ll have lived longer without a period than with it.

So much time, and so much for math done on fingers. So much for counting as a form of prayer. So much for fecundity, so much for blood.

So much for menstrual anxiety. I can’t say I miss it.