All my previous posts on here have only been ACX meetup notices (if you're in Phoenix AZ, you should come say hi!). However, recently my wife and I started co-writing a substack, like all the cool kids. Our meetup Discord told us that this was a particularly good article, and encouraged me to crosspost to lesswrong. Thus I present: our guide to NFP, because we have health concerns for hormonal birth control, and barrier methods feel lame.
The Marquette Method is one of the fanciest and premier ways to do cycle tracking and NFP to avoid pregnancy. However, clear online guides for this method are relatively scarce; they’re around, but mostly not conveniently located or well done. Marquette University, the people who invented this method (and run the flagship site Vitae Fertility), seem to like to keep their info pretty close to the chest. They don’t publish much in the way of detailed instructions, preferring to write in generalities, and they quite heavily push the necessity of paying them for a consultation to be taught the method. Lucky for us, it’s the 21st century, and we have deep research LLMs that can hunt down the original papers and publications describing this method and compile the sources for us. We did all the research and wrote up a guide for ourselves, and then figured we might as well enlighten the rest of the world by tidying up and publishing what we’d written for ourselves.
Our guide here only applies when you’re on a regular cycle, and not postpartum. The method requires some adjusting if any of the following are true of you:
You recently had your first period
You just had a baby
You’ve recently stopped taking birth control pills or other hormone contraceptives
You’re breastfeeding
You’re approaching menopause
You have irregular menstrual cycles
Your cycle is less than 26 days long or more than 32 days long
For everyone not in that exceptions list, our guide should suffice. The Marquette Method essentially feels like the Standard Days Rhythm Method, but using the Clearblue Monitor to increase precision and decrease accidental pregnancy rate from ~5% to <1% in perfect-use settings.
The Standard Days Method
The basic Standard Days protocol has you count the days in your menstrual cycle, with the first day of your period as day 1, and then counting up from there.
Here’s the basic Standard Days protocol:
The first day you bleed (spotting doesn’t count), is day 1.
On days 1-7, you’re not fertile, and you’re free to have unprotected sex.
On days 8-19, you’re fertile.
On day 20 until the end of your cycle (i.e. your next period), you’re not fertile.
When you get your next period, begin counting again from day 1.
The Marquette Method
The Marquette Method uses the Clearblue fertility monitor, which measures your urine for estrogen and luteinizing hormone (LH) to check your fertility status. The monitor is designed for conceiving, but with a few simple tweaks in use, its purpose can be inverted to avoid conception instead.
Set up the Clearblue monitor as normal according to the instructions. It will ask you to mark the first day of your cycle, and it will begin asking you to take urine samples on day 6. The monitor will usually ask for ten days of testing, though this may vary over the months as the system acclimates to your particular cycle length and biology — on your first use, it will probably test closer to 20 days as it gets a read on you.
Consider yourself fertile beginning day 6 (i.e. day 5 is the last day of free sex). Or, if you’ve got a slightly higher risk tolerance, you can follow the Standard Days Method and consider yourself fertile beginning day 8. The two-day difference comes from the risk tolerance levels between the Standard Days Method and the Marquette Method. About 10% of women with regular cycles are fertile by day 6; the authors of the Standard Days Method were willing to accept this low level of risk in their protocol, as every extra abstinence day reduces adherence. Marquette wanted a method that would be functionally impregnable; so they took a more conservative number of days — and given their methodology holds unintended pregnancy at <1% with perfect use — they’ve succeeded.
Once your estrogen begins to rise, the monitor will show high fertility (usually for about three days), you will be peak fertility for two days when your LH spikes during ovulation, and then you will usually have one day of high fertility after the two peak days. Generally, you’re infertile after three full days following the last peak day (e.g. if your last peak day was day 14, you’re safe beginning day 18). The extra cautious are sometimes counselled to wait until three consecutive low readings to make absolutely sure you’re out of the fertility window.
After six months, adjust your fertile window from beginning day 6 (or 8), to beginning on the earliest peak day seen in the last six cycles minus six (e.g. if your earliest first peak day was day 13, consider yourself fertile beginning day 7 (13 – 6 = 7); i.e. day 6 is your last safe day). This changes your fertility window from being based on population averages, to being based on your specific body’s patterns, thus increasing accuracy.
Once you have six months’ worth of data then, your protocol will look like this:
(For illustration purposes, I’m going to use day 13 as the earliest day of your first peak day in the past six cycles)
The first day you bleed is day 1; enter this into your monitor.
You can have free sex until day 6.
Fertility window opens day 7 (13 – 6 = 7).
Let’s say that month you have your last peak day on day 15.
Fertility window then closes on day 18 (15 + 3 = 18).
On day 19 you may have free sex again.
The Marquette Method’s Chance of Unintended Pregnancy
The chance of pregnancy with the Marquette Method is less than 1% per year with perfect use. Now, on typical use, the chance of pregnancy is ~5%. People worry about this, but you shouldn’t — provided you don’t have skill issues. Really, “Typical use” just means that you didn’t follow the instructions. This includes things like having unprotected sex when you know you’re fertile because you’re just so very horny. The trick is not doing that.
Postscript: Additions to the Marquette Method
Some sources will suggest that you can supplement the Marquette Method by tracking your cervical mucus, basal body temperature, or other such indicators. Do not do this. Adding additional fertility indicators actually lowers your success rate compared to straight Marquette. This is for two reasons. First, more indicators add complexity, and confusion can lead to mistakes. Second, and more importantly, self-control is hard; if you have multiple conflicting indicators, you’re likely to pick whichever one allows you to have sex in the moment when you’re horny, thus defaulting you to whichever indicator is least conservative in that instance — not a recipe for success. Stick with the simple and objective single metric.
Obligatory legal note: This post is offered for educational purposes only; it is not medical advice. The Clearblue Fertility Monitor is cleared by the FDA solely as an aid to achieving pregnancy; employing it to avoid conception is an off-label practice not evaluated or endorsed by the FDA. Always confer with a qualified clinician.
All my previous posts on here have only been ACX meetup notices (if you're in Phoenix AZ, you should come say hi!). However, recently my wife and I started co-writing a substack, like all the cool kids. Our meetup Discord told us that this was a particularly good article, and encouraged me to crosspost to lesswrong. Thus I present: our guide to NFP, because we have health concerns for hormonal birth control, and barrier methods feel lame.
The Marquette Method is one of the fanciest and premier ways to do cycle tracking and NFP to avoid pregnancy. However, clear online guides for this method are relatively scarce; they’re around, but mostly not conveniently located or well done. Marquette University, the people who invented this method (and run the flagship site Vitae Fertility), seem to like to keep their info pretty close to the chest. They don’t publish much in the way of detailed instructions, preferring to write in generalities, and they quite heavily push the necessity of paying them for a consultation to be taught the method. Lucky for us, it’s the 21st century, and we have deep research LLMs that can hunt down the original papers and publications describing this method and compile the sources for us. We did all the research and wrote up a guide for ourselves, and then figured we might as well enlighten the rest of the world by tidying up and publishing what we’d written for ourselves.
Our guide here only applies when you’re on a regular cycle, and not postpartum. The method requires some adjusting if any of the following are true of you:
For everyone not in that exceptions list, our guide should suffice. The Marquette Method essentially feels like the Standard Days Rhythm Method, but using the Clearblue Monitor to increase precision and decrease accidental pregnancy rate from ~5% to <1% in perfect-use settings.
The Standard Days Method
The basic Standard Days protocol has you count the days in your menstrual cycle, with the first day of your period as day 1, and then counting up from there.
Here’s the basic Standard Days protocol:
The Marquette Method
The Marquette Method uses the Clearblue fertility monitor, which measures your urine for estrogen and luteinizing hormone (LH) to check your fertility status. The monitor is designed for conceiving, but with a few simple tweaks in use, its purpose can be inverted to avoid conception instead.
Set up the Clearblue monitor as normal according to the instructions. It will ask you to mark the first day of your cycle, and it will begin asking you to take urine samples on day 6. The monitor will usually ask for ten days of testing, though this may vary over the months as the system acclimates to your particular cycle length and biology — on your first use, it will probably test closer to 20 days as it gets a read on you.
Consider yourself fertile beginning day 6 (i.e. day 5 is the last day of free sex). Or, if you’ve got a slightly higher risk tolerance, you can follow the Standard Days Method and consider yourself fertile beginning day 8. The two-day difference comes from the risk tolerance levels between the Standard Days Method and the Marquette Method. About 10% of women with regular cycles are fertile by day 6; the authors of the Standard Days Method were willing to accept this low level of risk in their protocol, as every extra abstinence day reduces adherence. Marquette wanted a method that would be functionally impregnable; so they took a more conservative number of days — and given their methodology holds unintended pregnancy at <1% with perfect use — they’ve succeeded.
Once your estrogen begins to rise, the monitor will show high fertility (usually for about three days), you will be peak fertility for two days when your LH spikes during ovulation, and then you will usually have one day of high fertility after the two peak days. Generally, you’re infertile after three full days following the last peak day (e.g. if your last peak day was day 14, you’re safe beginning day 18). The extra cautious are sometimes counselled to wait until three consecutive low readings to make absolutely sure you’re out of the fertility window.
After six months, adjust your fertile window from beginning day 6 (or 8), to beginning on the earliest peak day seen in the last six cycles minus six (e.g. if your earliest first peak day was day 13, consider yourself fertile beginning day 7 (13 – 6 = 7); i.e. day 6 is your last safe day). This changes your fertility window from being based on population averages, to being based on your specific body’s patterns, thus increasing accuracy.
Once you have six months’ worth of data then, your protocol will look like this:
(For illustration purposes, I’m going to use day 13 as the earliest day of your first peak day in the past six cycles)
The Marquette Method’s Chance of Unintended Pregnancy
The chance of pregnancy with the Marquette Method is less than 1% per year with perfect use. Now, on typical use, the chance of pregnancy is ~5%. People worry about this, but you shouldn’t — provided you don’t have skill issues. Really, “Typical use” just means that you didn’t follow the instructions. This includes things like having unprotected sex when you know you’re fertile because you’re just so very horny. The trick is not doing that.
Postscript: Additions to the Marquette Method
Some sources will suggest that you can supplement the Marquette Method by tracking your cervical mucus, basal body temperature, or other such indicators. Do not do this. Adding additional fertility indicators actually lowers your success rate compared to straight Marquette. This is for two reasons. First, more indicators add complexity, and confusion can lead to mistakes. Second, and more importantly, self-control is hard; if you have multiple conflicting indicators, you’re likely to pick whichever one allows you to have sex in the moment when you’re horny, thus defaulting you to whichever indicator is least conservative in that instance — not a recipe for success. Stick with the simple and objective single metric.
Obligatory legal note: This post is offered for educational purposes only; it is not medical advice. The Clearblue Fertility Monitor is cleared by the FDA solely as an aid to achieving pregnancy; employing it to avoid conception is an off-label practice not evaluated or endorsed by the FDA. Always confer with a qualified clinician.