Do ovulation calculators work when you have irregular periods?

Written by:, PhD, Founder and Inventor of the Proov test — the first and only FDA-cleared test to confirm successful ovulation at home.

Ovulation calculators are pretty popular these days, and they come in many forms — apps, algorithms, even built-in to some popular fertility testing devices.

But how do they actually work, and do you need to have regular cycles? What are the advantages and disadvantages of relying on them when trying to conceive?

Read on to learn all about ovulation calculators, and why you may want to consider other fertility tracking methods — especially if you have irregular cycles.

Do ovulation calculators work when you have irregular periods 

How do ovulation calculators work? 

Ovulation calculator” can refer to any app, device, or algorithm that tries to “predict” current fertility and periods based on past cycle data. This can be as simple as using your typical cycle length to count out to your next period, or as complex as using past dates of confirmed ovulation to try and guess at when future ovulation occurs.

Many are also referred to as “period tracker apps,” and most rely on the assumption that all women have 28-day cycles, ovulating exactly on day 14 and a fertile window between days 10-16. (Remember that cycle day 1 is the first day of your period.)

However, these assumptions are faulty. A recent study found that only 13% of women had a 28-day cycle, and ovulation is frequently later than day 14.

Another study tested 10 period tracker apps and found that different apps gave different predictions, even for the same person! The authors of that study recommended that an actual measure of ovulation should be used, not just using calculations to try and predict fertility. An app or calculator has no way to tell what’s actually going on in your body! 

Do ovulation calculators work when you have irregular periods

An ovulation calculator or app has no idea what's actually going on inside your body!

Ovulation calculators and irregular cycles 

By this point, you’ve probably figured out that if an ovulation calculator is assuming a 28-day cycle (or just assuming based on your past cycle lengths), it isn’t going to work very well for people with irregular cycles.

The average woman has cycle length fluctuations of around 3 days cycle-to-cycle, and an ovulation calculator can’t really account for that. If your cycles fluctuate more than that (or you rarely even have cycles), an ovulation calculator will basically be guessing. 

Irregular cycles can be due to polycystic ovarian syndrome (PCOS), endometriosis, thyroid problems, or a myriad of other conditions. Even though we call them irregular, they’re pretty common! For instance, PCOS is one of the most common causes of infertility and affects up to 12% of women

So if an ovulation calculator is only working based on past cycle data, and your past cycles are irregular or don’t really exist, there won’t be much to go off of. You may be asking then, how do I figure out when I’m ovulating (or when my next period is coming) if an ovulation calculator isn’t going to do it?

Do ovulation calculators work when you have irregular periods

Ovulation calculators ignore your unique hormone patterns

That’s where tracking your hormones comes in! Whether you’re trying to conceive or not, you can track your body’s unique cycle patterns and hormones.

Estrogen and luteinizing hormone levels can help predict when ovulation is approaching, and progesterone levels rising will confirm that ovulation has already occurred. Understanding these hormones is especially important with irregular cycles, since they can help make sense of an otherwise confusing situation. 

It’s key to track multiple hormones, too. For instance, women with PCOS and some other conditions may repeatedly have estrogen rises, and even the occasional luteinizing hormone (LH) surge, that don’t result in ovulation. Tracking estrogen and LH will help you determine when ovulation is likely, telling you the right time to try if you’re trying to conceive, but you should also confirm successful ovulation with a rise in progesterone.

How to actually predict and confirm ovulation

Fortunately, there are several easy, at-home ways to predict and confirm ovulation, all without ovulation calculators or even needing past cycle data. Some common methods include: 

Cervical mucus: In response to rising estrogen (usually about five days before ovulation), cervical mucus changes consistency and water content to allow sperm transport. Tracking cervical mucus is a good way to predict that ovulation is coming soon, but it can be influenced or obscured by hydration, intercourse, or illness.

Basal Body Temperature (BBT): Your body temperature rises after ovulation, and can be measured every morning to confirm that progesterone is rising. However, it can’t tell you whether or not ovulation was successful, just whether or not it happened.

Urinary Hormone Tests: You can also use at-home urine tests to get a better understanding of your hormone patterns. Proov Complete tracks all four major fertility hormones, and can tell you both if ovulation is likely and if it already happened (and whether or not it was successful). The Predict & Confirm kit is also a great choice for irregular cycles. And the Proov Insight App will take the guesswork out of when and how to test, based on your hormone levels and rather than a one-size-fits-all calculation. 

Do ovulation calculators work when you have irregular periods

You can also use at-home urine tests to get a better understanding of your hormone patterns.

(Note: the Proov Insight app is end-to-end encrypted and we never sell data.)

So there you have it — even for irregular cycles, there are a number of great and useful ways to determine fertility and the approximate time of ovulation. You can probably skip the ovulation calculators and period tracker apps, though. You’ll get more information by tracking your hormones yourself anyway!