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Luteal Phase Calculator

Created by Łucja Zaborowska, MD, PhD candidate
Reviewed by Anna Szczepanek, PhD and Jack Bowater
Based on research by
Bull JR, Rowland SP, Scherwitzl EB, Scherwitzl R, Danielsson KG, Harper J. Real-world menstrual cycle characteristics of more than 600,000 menstrual cycles.; npj Digital Medicine - Nature; August 2019See 1 more source
Sonntag B, Ludwig M. An integrated view on the luteal phase: diagnosis and treatment in subfertility.; Clinical Endocrinology; October 2012
Last updated: Jan 18, 2024

The luteal phase calculator is a simple tool designed to estimate the length of the luteal phase and to assess its normality.

But we won't stop there. We'll tell you what the threshold for the short luteal phase is, and we'll teach you how to calculate the luteal phase in menstrual cycles. 🧮

We'll answer two important questions:

  • How to count luteal phase from ovulation?
  • How to calculate luteal phase without knowing ovulation?

What is the luteal phase in calculators?

Let's start with the basics. What do we mean when we say luteal phase? What is it exactly, and why does it matter?

Let's take a look at the picture below:

Phases of menstrual cycle

As we can see, the menstrual cycle starts with the first day of the period and ends when the luteal phase concludes. The perfect menstrual cycle lasts 28 days, with ovulation occurring in the very middle of it. As a result, both the follicular phase and luteal phase should be the same length.

However, as we all know, nature is not perfect, and neither are we. Cycles of different women have different lengths, and that's totally fine - the length of the follicular phase is usually the one responsible for all these observed differences.

On the other hand, the luteal phase usually lasts the fixed number of 14 days. Some books say that this number should be identical for every woman - but there are plenty of studies which have already proved this statement wrong.

Why do we need the luteal phase length calculator?

Luteal phase plays an important role in female fertility - high concentration of progesterone during that phase allows the uterine lining to grow even more, preparing the area for the implantation of the embryo.

That's why a shorter luteal phase may cause lower concentrations of progesterone after conception, leading to a higher rate of miscarriages and a lower number of pregnancies.

A luteal phase deficit may be treated with Clomid. To learn more about a treatment for luteal phase deficit, visit Clomid calculator⏱️.

How to use the luteal length calculator?

It's the easiest task there is!

  1. Enter your ovulation date.

  2. Enter the first day of your period that followed the ovulation.

    You need to note both of these days during the same cycle.

  3. Yay! Your results are already here! 🎂 Our ovulation and luteal phase calculator will tell you straight away if your luteal phase is too long or too short.

If you want to track when you are ovulating over the next three cycles, use ovulation calculator.

How do I calculate the luteal phase from ovulation?

It's perfectly easy! If you already know your previous ovulation date and the first day of your period, you'll need precisely one formula!

Here's the equation featured in our luteal length calculator:

Luteal phase = First day of period date - Ovulation date

Your final result will be given in days.

Happy with the average luteal phase length calculator? Would you like to know more about human fertility? 🤔 Take a look at our other related tools, such as sperm analysis calculator and pregnancy test calculator.

How do I calculate luteal phase without knowing ovulation?

Unfortunately, you need to know the day of your ovulation in order to be able to calculate the luteal phase in your menstrual cycle.

Here's a list of ways to find out about your ovulation date:

  • Use an ovulation predictor kit;
  • Note the change in the appearance of the cervical mucus;
  • Perform daily measurements, and note sustained increases in body temperature, not caused by infection or alcohol; and
  • Finally, use the Omni Ovulation Calculator 😊


How to count your luteal phase?

Your luteal phase starts right after the day of your ovulation. Ovulation can be detected by either use of a thermometer (peak in body temperature) or special home tests.

Your luteal phase ends on the very first day of your period.

If you note both of these days in a single month, all you need to do is count the days between them. 👍

What is a short luteal phase?

The short luteal phase occurs when the part of the menstrual cycle between ovulation and period lasts 11 days or less.

💡 A short luteal phase may impair short-term fertility and is more common among smokers.

How to find out the luteal phase length?

Discovering whether your luteal phase is too long or too short isn't tricky- you may use one of the luteal phase length calculators or quickly count days between your ovulation and the first day of your next period.

What is a long luteal phase?

The long luteal phase occurs when the part of the menstrual cycle between ovulation and the period lasts more than 17 days.

The long luteal phase might be caused by:

  • Pregnancy;
  • Underlying hormonal disease; and
  • PCOS (Polycystic ovary syndrome).
Łucja Zaborowska, MD, PhD candidate
Ovulation date
First day of period
Luteal phase length
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