As a lifelong self-improvement and learning freak, and a fan of number crunching, I’ve been following the Quantified Self movement with some interest. There’s tons of research to show that the simple act of keeping records of what we’re doing – whether it’s a food diary, exercise log, or a timesheet – results in positive behaviour changes. It also, of course, keeps things pretty real; if we’re wondering what happened to our 6-minute mile or our waistline, we can find the answer in our data.

While I’ve lived by the billable hour (and therefore, by timesheets) for many years, my favourite experiment with Quantified Self began as an attempt to manage something far more personal: my menstrual cycles.

You see, like many women, I went on The Pill in my teens, and as a result I had an extremely predictable 28-day cycle that was artificially controlled by the hormones I was ingesting on a daily basis. It was nice, and pleasant, and made my periods so incredibly predictable that I lived through my twenties without really giving them (or the risk of pregnancy) a second thought.

Then one day, I read the umpteenth news story reporting on research linking prolonged, continual use of The Pill to a higher risk of cervical cancer, and I decided it might be worth going off The Pill for a while and seeing what life was like without extra hormones flowing through my body. And that meant switching to higher-risk contraceptive options.

I’d read Toni Weschler’s Taking Charge of Your Fertility (a book I wish they’d teach to all high-school age girls, and ideally boys as well), so I knew that by tracking your cycle, you could identify the day you ovulated, and thereby calculate all manner of other information, including when you were – and weren’t – fertile. So I printed off copies of Weschler’s PDF chart template, and got to work.

For about ten years, the first thing I did every single morning was to reach over to the side of my bed, pick up my thermometer, and take my basal body temperature before I got out of bed. Then I’d record the information on my chart, and go about my day. (There are other indicators you can track, and I charted those for a while, too, until I knew my cycle well enough to go by temperature alone.)

The process was not only deeply informative, but it also changed my relationship with my periods. For starters, my period stopped being an unwelcome surprise and became a predictable – and much more welcome – event. And I also learned that my cycles were much more regular than I thought. The act of recording data every day (or nearly every day) meant that I stopped approximating when my last period was – I could now simply check the dates. (Part of the “surprise” each month was that my cycles are shorter than average, so if I’d been expecting my period every 28 days, it was consistently arriving a couple of days early.)

The thing is, knowing you have a short cycle is valuable not only so that you can plan what days to carry your DivaCup and ibuprofen in your handbag – it also matters a lot if you’re aiming to avoid (or achieve) pregnancy – because while an enormous number of doctors, books, and websites will tell you that ovulation occurs on Day 14 of your menstrual cycle, that’s simply not true. That’s an average, but in reality ovulation can happen earlier or later – Day 14 is just an approximation.

Since your most fertile days span your date of ovulation, it helps a lot to know when they actually fall.

With the data I was charting about my basal body temperatures, I was able to determine when I was ovulating – this in turn helped me learn to predict which days in my cycle I was least likely to conceive, which made birth control decisions a lot easier.

Of course, years later, when my partner and I decided to try and have a baby, I went back to charting my cycles and temps, and gathered data for a few months using an iPhone app (much more convenient than the old paper-and-pen method!). Once I was certain the data was showing consistent patterns, I calculated my most fertile days and loaded them into a shared Google Calendar. (This step had two important effects: one, it allowed my partner – who travels a great deal on business – to refer to it when planning his travel dates, and two, it released me from the responsibility of dreaming up seductive ways of whispering to him that I was ovulating. We both knew when the dates were, and could therefore take joint responsibility for keeping the mood at home flirty.)

Between the charting and some very good fortune (especially those fertile Scottish farmer genes that I inherited), I had a shockingly easy time getting pregnant: At the age of 39, I found myself pregnant after just one cycle of “trying.” What was a little less easy was wrapping my head around what the data were all pointing to: that I was indeed pregnant, already. My cycle tracker showed that my period was four days late; I’d had 16 days in a row of consistently high basal body temps. On day 16, I rolled over and told my partner (an early adopter & evangelist for FitBit, who passionately tracks the number of steps he takes every day), “Another high temp,” and he replied with, “You’re pregnant. Just go to the drugstore and get a pregnancy test.” Sure enough, the test confirmed what he already knew – and what I had to accept the numbers were telling me.

Kinda wish I’d been wearing a heart rate monitor that day.

While I was taken aback by how easy it had been to get pregnant, my partner pointed out to me that I had done way more homework than the average woman: I had ten years of charts to go by, and a deep level of book-learning on the subject of fertility and ovulation that gave me a leg up on many people. (There’s a lot of misunderstanding out there about the timing of ovulation – the aforementioned “Day 14” stuff – and about how to time sex to maximize your odds of getting pregnant. A lot of people believe you should have sex the day you ovulate, when in fact it’s best to have sex on the days leading up to ovulation, since the egg only lives 24 hours after ovulation, and sperm can live up to 5 days.)

I’d love to see what impacts cycle tracking could have if it were more widespread. The amount of information I’ve gleaned over the years from this small habit has been pretty staggering, and it has made me tremendously confident in understanding my body and my fertility. With birth control (both in the sense of contraception, and controlling when and how we want to have babies) such a central concern for women around the world, the potential for better lives through charting is huge.