How to predict the arrival of your next period

My Hormonology

How to predict the arrival of your next period


Have a “short” menstrual cycle (one that’s shorter than 28 days)?

Have a “long” menstrual cycle (one that’s longer than 28 days)?

Have a cycle that varies in length from month to month?

You can still use Hormonology to find out what your mood, energy and more will be every day of your cycle.

And, also useful, you can always know when you’ll get your period–regardless of how long your cycle is. That’s right–no more guessing, no more surprises.

How? Math. Very, very simple math.

The female cycle formula

The reason you can use Hormonology and predict your next period date regardless of how many days are in your cycle is because of the way your menstrual cycle is set up:

The first “half” of your cycle–from the first day of your period through ovulation–is the only part of your cycle that varies in length.

The second “half” of your cycle–from the day after ovulation through the day before your next period–is generally a stable 14 days (barring extreme stress, illness, medication or perimenopause). That’s because once ovulation occurs, an inner clock inside your body begins to tick down either to your period or pregnancy. If you didn’t get pregnant, then the clock stops at 14 days, and you get your period.

This means that if you have a 28-day cycle, it’s because the first half of your cycle was 14 days.

If you have a shorter cycle, let’s say 26 days, it’s because the first half of your cycle was 12 days.

If you have a longer cycle, for example, 30 days, it’s because the first half of your cycle was 16 days.

So, the key is to pinpoint when you ovulate (I’ll get to how you do that in a minute), then count down to 14 days. That’s when you’ll get your next period.

Adapting your cycle to Hormonology

Now that you know how your menstrual cycle works, here’s why Hormonology adapts to every cycle length:

Hormonology shows you how your hormones impact you every day of your cycle. It shows you this on a daily basis and it also breaks your cycle up into four easy chunks–Week 1, Week 2, Week 3 and Week 4.

Week 1 and Week 2 are the first half of your cycle–from the first day of your period through ovulation. On these days, your hormones are doing the same thing–estrogen is climbing higher and higher. So, no matter how long or short this first half of your cycle is, you’re really experiencing the same hormonal effects. They just get more and more intense as you approach ovulation, for instance, your mood, energy and libido steadily increase.

Week 3 and Week 4 are collectively 14 days (Week 3 last 8 days, Week 4 last 6 days). The hormone situation going on during these weeks are a bit more complex with estrogen falling, then rising, then falling again, and progesterone rising and falling. But, it doesn’t matter, because for the sake of Hormonology and predicting your period, you’ve got 14 days in this cycle phase.

Detecting ovulation

You may have thought that detecting ovulation was only important for getting pregnant or avoiding pregnancy. But, as you can see, it’s a important signpost that tells you where you are in your cycle.

So, how can you tell when you’ve ovulated?

There are a few physical symptoms you can look for, which include feeling pain (called “mittelschmerz”) in either ovary and seeing egg white-like vaginal fluid. However, I prefer to use ovulation detection tools since they’re far more reliable. These include:

  • Basal thermometer: It detects a subtle rise in your body temperature that occurs at ovulation due to progesterone.
  • Ovulation microscope: It measures salt in your saliva, which peaks shortly after ovulation.
  • Urine strips: These measure the level of a certain hormone (luteinizing hormone) that peaks right before ovulation.

You can find links to these ovulation detection tools with links to Amazon on my Recommendations page.

Your egg is the magic 8-ball

Now that you know how to detect ovulation and that ovulating means there are 14 days left to your cycle, you’ll always be able to accurately predict the ups and downs of your moods, energy and more using Hormonology. And, you’ll be able to stock up on whatever menstrual aids you use in time for your next period!

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