How To Always Know When Your Period Is Coming Even With An Irregular Cycle

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If you have an irregular menstrual cycle that always leaves you guessing about when your next period will arrive, then you need to learn this simple trick! I’m no stranger to irregular cycles, with cycles that range from 32 days to 55 days and anywhere in between, but I always know when my period is coming, and without relying on an app to make dodgy predictions for me. Keep reading to find out how I do it!

I’m currently on Day 44 of my cycle and my period just arrived (so I guess that makes it Day 1 again!) I’m not surprised, I knew my period was coming today. An app didn’t predict this for me, nor are my cycles always 44 days long. Far from it! I actually have irregular cycles, but I’m never caught off guard by the arrival of my period. I always know when it’s coming and with around a two week lead time.

The key is knowing when I ovulate. Before I started tracking ovulation, I was always flying blind in my cycle. Now that I track ovulation, I always know where I’m up to. And this handy hack is helpful for all cycles, whether they’re regular or irregular. If you want to always know when your period is coming, even with an irregular cycle and without relying on an app to make a prediction for you, then keep reading!

Ovulation is the main event of the cycle

I’ve said it before and I’ll say it many times again…ovulation is the main event of the menstrual cycle. Which is why it is the key to always knowing exactly where you’re at within your cycle.

Once you can confirm ovulation has occurred, then you know your period will soon be on its way. Unless of course you’re pregnant. That’s because, after ovulation, the only two options are period or pregnancy!

Think of your menstrual cycle in two phases:

  1. Pre-Ovulation; and
  2. Post-Ovulation


The Pre-Ovulation phase (also called the follicular phase) spans from day 1 of your cycle, that’s the first day of full blood flow on your period, through to ovulation. This phase of the cycle could be any number of days long.

It is typically represented as being 14 days long by text-book standards (you know the 28 day cycle, ovulate on day 14 BS) but in reality it could be much longer than that! It will be however long it takes your body to ovulate.

The time it takes your body to ovulate is unique to you and can even vary from cycle to cycle. The timing of ovulation can also be impacted by things such as illness, stress, travel, medical conditions and more.


The Post-Ovulation phase (also called the luteal phase) spans from ovulation until the day before your next period begins and it’s much more set in length.

Once ovulation happens, the egg is released and the body is preparing for a possible pregnancy.

If pregnancy does not occur then the uterine lining will begin to shed within 10 – 16 days of ovulation, resulting in your period arriving.

That means, once you have confirmed ovulation, and assuming you are not pregnant, you can expect your period in the next 10 – 16 days.

10 – 16 days sounds like a big range, but that’s just a range across everybody, you’ll likely find that your luteal phase will be a similar length each time.

Taking my own cycle as an example, my luteal phase is usually 12-14 days long, which means that I know to expect my period within 12-14 days of ovulation.

This is how I always know when my period is coming, even with an irregular cycle!

How NOT to Confirm Ovulation

So you might be wondering how to confirm ovulation for the purpose of knowing when your period is coming? Well stick with me, I’m going to get into that!

But first things first, let’s talk about how NOT to confirm ovulation.

It’s super important to understand that the only way we can confirm ovulation with certainty, aside from an ultrasound, is to track the signs given by our body. Which we will talk about in just a moment. But what this means is:

  • We cannot confirm ovulation by relying on our period tracking app telling us we have ovulated or giving us any sort of messages, lights or indicators that we are fertile or not fertile;
  • We cannot confirm ovulation by counting days from our last period or assuming ovulation occurs on a set day each cycle e.g. cycle day 14;
  • We cannot confirm ovulation from a positive Luteinising Hormone (LH) Test;
  • We cannot confirm ovulation by a feeling we get like a twinge in the ovary;
  • We cannot confirm ovulation by wet cervical mucus alone.

The only way to confirm the exact moment of ovulation is via an ultrasound but we can use observations of our cervical mucus and the tracking of our daily basal body temperature to really hone in on the approximate time of ovulation and to confirm with certainty once it has happened.

Basal Body Temperature (BBT)

Basal body temperature is the body’s temperature at rest, after at least 3 hours of uninterrupted sleep or rest. Also referred to as waking temperature.

Why do we care about our basal body temperature?

Well, interestingly, in 1868 a Doctor in London discovered that the temperature chart of females in their fertile years differed to that of men – the females temperature rose to a higher level approximately half way through the menstrual cycle.

In 1904 a Dutch gynaecologist expanded on this by noting that the rise from the lower temperatures to the higher temperatures was related to ovulation.

What happens is, after ovulation, a temporary endocrine gland called the corpus luteum is formed from the follicle that released the egg at ovulation.

The corpus luteum produces the hormone progesterone and it is this release of progesterone that causes a rise in the basal body temperature.

If we track our BBT every day and chart it on a graph, we can identify once this temperature rise occurs and provided it stays risen, we can use this as an indicator that ovulation has occurred.

BBT is a retrospective indicator of fertility. It gives us no warning of ovulation approaching because it only rises after ovulation.

If you only want to confirm ovulation after the fact, which is all you need to do for the purpose of knowing when your period is coming, then you can track BBT on its own.

If you want to get a little more insight into exactly what’s going on in your cycle and have some warning of approaching ovulation then you can also observe and track your cervical mucus.

I personally track both BBT and cervical mucus as part of the Sympto-Thermal method of fertility awareness that I use as my method of contraception to avoid pregnancy naturally. This is beyond the scope of this article and the information I share in this article is not sufficient to enable you to use fertility awareness as a form of birth control.

Confirming Ovulation

The only way to confirm ovulation in real time is via an ultrasound but we can use our daily basal body temperature to confirm ovulation retrospectively.

By taking our BBT each day and plotting it onto a chart, we can confirm ovulation has occurred once our temperature has risen by 0.2°C and sustained that temperature rise for at least 3 days and then stays risen for the rest of the cycle.

The rise in basal body temperature will look something like this on a chart. The aqua dots plot the BBT reading each day.

You can see that on cycle day 17, the temperature rose and stayed risen for the rest of the cycle. This confirms that ovulation occurred around this time and the luteal phase (post-ovulation) began on Day 17 and continued until Day 31.

This chart is from the Read Your Body app which is the only app I use and recommend.

What You Need to Track Your BBT

The tools I use to track my cycle are the Tempdrop and Read Your Body app.

The Tempdrop is a wearable sensor that monitors your basal body temperature while you sleep. It eliminates the need to wake up at the same time every morning to take your temperature and filters out disturbances that otherwise may impact your temperature reading. The Tempdrop is an investment and is definitely not a requirement for tracking your BBT, but it is nice to have as it does make the process a lot easier.

For 10% off Tempdrop use the code TDBETTER10

If you’re not ready to make an investment into a Tempdrop, you can pick up a basic basal body thermometer, also called a digital ovulation thermometer at your local drug store or online. It shouldn’t set you back much more than $20 (AUD).

The Read Your Body app is not your average period tracking app. It is a comprehensive tool that allows you to input all of your own data and produce a chart that you can interpret yourself. It does not make predictions of your fertile window or ovulation date or period due date. It’s run by a non-profit and your personal data is not sold to third parties. This does mean it’s a paid app but it’s worth it. You can download it from the app store here.

If you want to keep it simple or start a wholesome mindful practice of charting your cycle, you might like to chart on paper. You can download paper charts online or even find some beautiful paper charting journals.

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