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Determining the length of your menstrual cycle (period cycle) can be helpful for many reasons. For example, if you plan to take ovulation tests, you will often need to calculate your cycle length to help you determine the time to start testing.
In this article, you’ll learn how to count your
period cycle length.
Tools Needed to Count Menstrual Cycle Length
- Calendar (to
count your cycle)
- Calculator (to
track the length of your cycle for at least three months)
- Dates of
when your recent periods started (preferably at least 3 cycles worth of
dates, which you will average together)
Here are some examples of recent period start dates:
- Period
started: October 31, 2022
- Next
period started (November 29, 2022)…which gives us one month
- Then
the next period started (December 29, 2022)…which gives us two months
- And
finally the next period started (January 27, 2023)….which gives us three
months
You could go beyond that to six month’s worth of period
dates or even a year and then average it out. The more dates you use, the
better; but three months will work just fine to determine your average
menstrual cycle length.
How to Calculate Period Cycle Length (Menstrual Cycle)
To calculate menstrual cycle length, you’ll start with the
first month you’re using for your period dates, and look at the day your period
started. This first day that your period started is counted as cycle day 1.
Note: the day you count as the actual day your period starts
is the day you had an actual flow of menstrual blood, NOT just spotting.
Once you have cycle day 1, you keep counting up until the
day BEFORE your next period started, because this is the LAST day of
that cycle.
Example: The first month your period started was on
October 31, 2022, and your next period was November 29, 2022.
In this example above, we’ll count October 31 as cycle day
one, and keep counting to include November 28, 2022 (the day before the second
month’s period that started on November 29). This will give us the cycle length
for that month to be 29 days.
Then count the cycle length for the next two months.
Second month: November 29-December 28: counting from
November 29 day one to December 28 which is the last day of that cycle (it ends
the day before the next period started): 30 days
Third month: December 29-January 26. This will give
you a period cycle length of 29 days:
Calculating Menstrual Cycle Length Average
Again, here are the cycle lengths for each month we
calculated:
- First
month: 29 days cycle length
- Second
month: 30 days cycle length
- Third
month: 29 days day cycle length
To calculate menstrual cycle length average, add all three
cycle lengths together (29+30+29=88). Next, we divide by the total number of
months we used (3), and we get an average menstrual cycle length of 29.33 days
(rounded to 29 days).
Therefore, in the example above, we had an average menstrual
cycle length of 29 days.
Menstrual Cycle Questions and Answers
What should a normal menstrual cycle be? A
normal menstrual cycle should last anywhere between 21-35 days, and it can vary
month to month. For example, some months could be 28 days long, some may be 27
days long, or some may be 26 days long, but it’s still considered normal
because it falls within 21-35 days range. The average menstrual
cycle length is around 28 days.
What is considered an irregular menstrual cycle? If
your cycle is less than 21 days or greater than 35 days, it is usually
considered irregular. This can be happen if you are missing menstrual cycles or
if the bleeding portion of your period is lasting longer than 7 days (it
should last 3-7 days with an average of 5 days). Therefore, counting your cycle
length is important to help you determine if your menstrual cycles are normal.
Why do you want to know your cycle length? It
can be beneficial to know the length of your menstrual cycle for several
reasons. For example, it helps you determine whether your cycle is regular or
not. It can also help you track when to expect your next period if you want to
avoid certain situations (such as swimming) while menstruating (bleeding).
Finally, it can also help track ovulation, which tends to
happen 14 days after the start of your period (for a typical 28-day cycle).
Knowing the time of ovulation can help increase chances of pregnancy or could
even be used as a birth control method known as the “rhythm method” to prevent
pregnancy. However, keep in mind that the rhythm method is not 100%
reliable, and pregnancy could still occur.