how to calculate ovulation with irregular periods

How To Calculate Ovulation With Irregular Periods When Trying To Conceive

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If you’re wondering how to calculate ovulation with irregular periods because you’re trying to conceive, I know the struggle.

In fact, it took my husband and me 18 long months to conceive our first son.

A lot of those months were wasted though.


Because we completely missed my ovulation (a.k.a my fertile window) due to my irregular cycle. And TIMING is everything when you’re trying to get pregnant.

I was tracking my cycle with a fertility app, but I didn’t realize that calculating ovulation with irregular periods takes a lot more attention to detail and patience than I was giving it.

I had to learn this the hard way.

Let me explain:

Unless you have a perfect 28 day cycle every month, a fertility app isn’t going to accurately PREDICT your ovulation without a lot of input from you. (It will show you when you actually ovulated though after you log your period. But of course that’s not helpful after the fact.) This is because the app relies heavily on cycle length to predict when you’ll ovulate.

I believe I could have gotten pregnant much faster with my first baby if I had done a more thorough job of tracking my cycle to calculate my ovulation (like I did with my second baby) .

So if you’ve been asking yourself:

How do I calculate ovulation with irregular periods?

I’m going to tell you how you can do this in a fertility app the right way and avoid the mistakes that I initially made for months.

Here are the 4 things I wish I had done differently if I had known how to calculate ovulation with irregular periods from the start.


I am NOT a doctor. This is just my experience. Please see your medical provider if you’re experiencing difficulties conceiving.

How To Calculate Ovulation With Irregular Periods Through Daily Tracking

When I first started using a fertility app to track my cycle, I was basically just plugging in the calendar dates when I got my period.

I guess I thought that the app could calculate my ovulation based on my cycle length alone.

Boy, was I wrong.

For months the app would make a prediction for my fertile window (the days you can conceive) based on my previous cycle lengths.

But when you have an irregular cycle that is 36 days one “month”, 48 days the next and 54 days the following “month”, this just doesn’t work.


If there is no other data to go off of, the app will always calculate your fertile window to be around 14 days prior to your period.

So if your last cycle was 36 days, the app will assume your next cycle to be of similar length.

Maybe it will. But us irregular gals, aren’t usually so lucky.

So the app will calculate ovulation around cycle day 22 for the following month based on last month’s 36 day cycle.

When you’re next cycle actually ends up being 48 days though, and you centered your baby making around cycle day 22, you’ll come to find out when you get your period that you actually more likely ovulated on cycle day 34.

Way off!

So unless you and your partner are having sex often, it is super easy to miss that short three day window of opportunity.

This happened to me more times than I want to remember.

That’s when I realized that I needed to take the app’s predictions with a grain of salt each cycle and instead, use it as a tool to learn my body.

Once I started paying close attention and tracking every day I got much closer to figuring out my body’s way of saying,

“HEY! I’m ovulating!”

Things like moods and symptoms (headaches, cramps, acne, pelvic pain, tender breasts, etc)…

…these are things that might have clued me (and the app) in about the workings of my body’s reproductive system sooner.

And ultimately, calculated my ovulation predictions a bit more accurately.

So tune into your body every day and take a few minutes to log all relevant information.

Track Cervical Mucus

Even though I had started tracking my moods and symptoms daily, I still wasn’t tracking one of the most fertility-telling signs my body was giving me:

Cervical mucus (CM).

Why is this sooooo important?

CM changes in consistency during the course of your cycle from a non-fertile state (creamy and sticky like school glue) to a fertile one (clear and stretchy like egg whites).

If only I had known this much sooner!…

…and looked for it!

You might be wondering:

How do I track my CM?

At first, I thought I could track my CM correctly by simply looking in my underwear every day.

But this turned out to be a mistake.

After months of doing this and looking back at my recordings where the type of CM didn’t line up with when I was actually fertile (about 14 days prior to period), I knew I was doing something wrong.

Unlike “school glue” CM, turns out it is hard to see “egg white” cervical mucus (EWCM) in your underwear.

Maybe this is just me, BUT…

I logged this as “no CM” many times essentially missing the fact that I was in my fertile window.

Much to my apprehension, I began tracking my CM in a more accurate manner…

Yep, I just checked myself “down there” every day by inserting a clean finger into my vagina.

Not super fun. But it quickly became part of my daily morning routine.

And it was worth it as it gave me a whole new awareness of my fertility.


It led to us having our baby boy!

I remember seeing the EWCM for the first time by this method. It was like a light bulb went off in my head.

I get it now. I know what it looks like when I’m fertile.


If you’re not seeing a lot of EWCM, you can always use a sperm friendly lube (like this one here).

It mimics your body’s own EWCM to help the sperm travel to your egg.

We used it in the hopes of giving the sperm an extra boost anyways. And it worked for us!

But of course, the point of checking your CM is to identify that you are in your fertile window in the first place.

I can’t tell you enough what a huge discovery this was for me.

It was hands-down the best way to tell when I was fertile and when I wasn’t.

For one, logging my CM correctly in the app made the predictions for my fertile window more accurate.


Having the visual confirmation of the EWCM made it so much less likely that I would miss my fertile window in the event that the app was a bit “off”.

Track Cervical Position

Another tangible sign of ovulation that I wish I had known about and tracked from the beginning is cervical position.

What do I mean by this?

Just like CM changes throughout your cycle, the position of your cervix and how it feels to the touch changes as well.

While you’re checking your cervical fluid, you can kill two birds with one stone and check your cervix at the same time.

So what are you looking for when you do this?

When you are most fertile, your cervix will feel soft, high, open, and wet (you can remember this as S.H.O.W.).

At other stages of your cycle, your cervix will be more firm, lower and closed.

It may take some time to figure out what your cervix feels like at each point of your cycle.

I found that using the notes section of the app was really helpful for describing this in addition to logging, for example, just:

  • Medium position
  • Firm
  • Closed

That’s because at first, you might not realize what these things really feel like until you’ve gone through a whole cycle or two checking most or every day.

Notes are best!

Once you track it enough though, you’ll likely have that “ah hah” moment like I did.

EWCM… check! Ok, my cervix is so high that I can’t find it!

It’s baby making time.

As laborious as this all may seem, it really is worth the trouble if you are struggling to calculate ovulation like I was.

Confirm Ovulation With Quality Test Strips

In addition to tracking your moods, symptoms and cervix each cycle, predicting and tracking your ovulation with test strips is a must.

The reason I say “in addition to” is because I made a couple of mistakes with this.

My first mistake is that I wasn’t tracking any of my symptoms or CM with my irregular cycle, so I had no clue when to start using the test strips.

I was either starting too early and using a lot of test strips (wasting money) or starting too late and had already missed the window.

AND I was using test strips that weren’t very good quality, in my opinion.

These are the ones where you pee on the stick and determine that you’re fertile by how dark the line is.

I could never quite tell which day was best. Is the line darker today than yesterday? I found it confusing.


Who wants to pee on these every day and line them up to compare with the previous days?

Not ideal.

I finally started using these digital ovulation tests, that give you a smiley face when it’s high time for baby making.

Again, I definitely wasted many of these tests as well by not knowing when to start peeing on them.

But, once I started tracking my other symptoms and CM, I only had to use a few of these each cycle before I got the smiley face.

It was such a relief to know with 100% certainty that I was in my fertile window.

No more missed opportunities.

This is also one of the best things you can log in your fertility app each cycle to make the app’s predictions for your fertile window more accurate.

Don’t be like me and log your ovulation incorrectly for months because you couldn’t read the test strips right.


Do yourself a favor and get these smiley face tests.

You’ll thank yourself later 🙂


If you’re struggling to calculate ovulation because you have irregular periods, I hope you’ll implement these four tracking strategies.

But just because you identify your fertile days and make the most of them, doesn’t mean you’ll get pregnant.

Did you know that there’s only a 20% chance that you’ll conceive each cycle?

While timing can be half the battle, there’s always more you can do to increase your chances of getting pregnant.

You can read more about this in this post:

How To Get Pregnant Fast With Irregular Periods

Best wishes to you in your journey.

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