What if you don’t have a 28-day menstrual cycle?

What if you don’t have a 28-day menstrual cycle?

Having trouble figuring out which menstrual cycle phase you’re in or when your period will arrive because your cycle is longer or shorter than the average 28 days, your cycle varies in length or you have no uterus, but do have ovaries? It’s easy to figure it out! Read on for the simple method….

If you want to know which phase you’re on in your menstrual cycle or when your period will be arriving, there’s an easy trick to figuring it out.


It works for healthy cycles of any length: 28 days, longer than 28 days, shorter than 28 days, and even cycles that vary in length from month to month.


It also works if you have no uterus, but you do have healthy functioning ovaries.


All it takes is pinpointing when you ovulate.  That’s because your cycle is split into two “halves”–and ovulation plays a key role in figure out which half you’re in.

First half of your cycle

This is called the “follicular” phase because a follicle matures in your ovary. This phase starts with the first day of your period (Day 1) and lasts until ovulation.

An important cycle clue to know about your follicular phase: This is the part of your menstrual cycle that varies in length. The first “half” of your cycle determines just how long your whole cycle will be.

This means if you have a menstrual cycle that lasts 28 days, this first “half” of your cycle typically lasts 14 days. So, ovulation would be on Day 14. However, if you have a cycle that’s less than 28 days, this part of your cycle is shorter than 14 days, so your ovulation day will be sooner. (For example, in a 26-day cycle, ovulation day would be on Day 12.) And if you have a cycle that’s longer than 28 days, this part of your cycle is longer than 14 days, so your ovulation day will be later. (For example, in a 30-day cycle, ovulation day would be on Day 16.)

Second half of your cycle

The day after you ovulate, you enter the second half, or “luteal” phase, of your cycle. It gets its name from the hormone progesterone, which is produced by a substance in the ovary that’s left behind after ovulation called the corpus luteum. This phase lasts until the day before your next period.

An important cycle clue to know about your luteal phase: It’s generally a stable set number of days that does not vary in length. 

This phase is typically 14 days in most menstrual cycles. That’s because once ovulation occurs, a clock inside your body begins to tick down either to your period or pregnancy. If you didn’t get pregnant, then the clock stops and you go on to get your period. (Note: In some, this phase can be slightly shorter or longer, such as 12 days or 15 days, but the luteal phase still tends to be a stable set number of days from cycle to cycle.)

What this means for you

Thanks to these cycle clues, you can always know where you are in your menstrual cycle:

  • When you get your period, you’re in the first half.
  • The day after you ovulate, you’re in the second half.
  • Then all you have to do is count down to 14 days (or the number of days in your luteal phase if it’s different). And that’s when you’ll get your next period.


The above are all general rules. Because the menstrual cycle is impacted by other processes going on in your body, this predictable pattern can be thrown off, for example, by stress, illness or medication. Also, the above applies to healthy menstrual cycles. If you are challenged with a condition that impacts hormones or the menstrual cycle, such as polycystic ovarian syndrome, then naturally these rules would not apply.

To figure out when you ovulate, check out the ovulation tools below

My Hormonology
My Hormonology
My Hormonology

Learn how your hormones impact you every day of your cycle in 28 Days: What Your Cycle Reveals About Your Moods, Health & Potential by Gabrielle Lichterman

The award-winning book that launched the cycle-syncing and hormone awareness movement

My Hormonology

How to determine when you ovulate

There are certain physical symptoms you can look for, which include feeling pain in either ovary (called “mittelschmerz”, which is German for “middle pain”) and seeing vaginal fluid that resembles raw egg white. However, there are ovulation detection tools that are more reliable.

My Hormonology

Basal thermometer: This special thermometer detects a subtle rise in your  body temperature that occurs at ovulation (and throughout your luteal phase) due to elevated progesterone. To use: Take your temperature every day once you wake up, but before you get out of bed. When you notice a rise in temperature of one-half to one degree in the middle of your cycle, it’s a sign that you’re ovulating.

My Hormonology

Ovulation microscope: This lipstick-sized reusable microscope measures the amount of salt in your saliva, which peaks shortly after ovulation. To use: Dab a little saliva on the lens, allow to thoroughly dry, then look through the microscope. If you see dots, you’re not near ovulation. If you see dots and lines, you’re nearing ovulation. If you see ferns, you ovulated the day before.

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Urine test strips: These disposable strips measure the level of luteinizing hormone (LH) in your urine. The amount of this hormone that your body produces surges one to one-and-a-half days before ovulation. To use: Simply pass the strip through your urine stream. Then, wait for the strip to indicate the level of LH in your system. When it peaks, you’ll be ovulating within 24 to 36 hours.

My Hormonology

Tracking every day of your cycle is easy with the Hormonology Menstrual Cycle Tracker Journal by Gabrielle Lichterman

12 sets of cycle trackers (equaling one year), more than 70 categories to track, add your own categories, 100% private

My Hormonology
My Hormonology

Important: Please do not use the information about ovulation on this web page as a sole form of pregnancy prevention. If you do not use birth control (such as condoms), you can get pregnant on the days leading up to, the day of and the day after ovulation. That’s because sperm can survive within your body for up to five days and your egg can survive up to 48 hours.

Do you always ovulate on the same day of your cycle, so you’re not worried about birth control on the other days in your cycle? Not so fast: Your usual ovulation date could have shifted due to stress, illness, medication or another factor, which means that even if you tried to calculate your most fertile days, your body could have made other plans, leaving you at risk.

So, please use an effective and safe form of birth control when trying to avoid pregnancy.

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