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Why does my period date change every month?

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

Your period date changing every month is not as uncommon as you think it is. Period dates vary. You're likely not going to get your period on the same date as the previous one due to changes in menstrual cycle, which ranges from 21-35 days.

It might occur more or fewer days than the actual day, and there's absolutely nothing wrong with it. Periods, during the first couple of years of menstruation, are often irregular due to the development of a delicate hormonal balance that leads to a regular cycle. 

However, if after years of regular cycles, your period falls completely out of range of your regular cycle, then you may ask yourself, "Why is my period irregular?" and you should consult a doctor. 

In this blog, we'll address all the possible causes of change in period dates, solutions, and what you can do to maintain a regular cycle. So, what causes change of date in menstruation? Let's explore. 


Reasons Why Your Period Date Changes Every Month

1. Stress

The impact of stress on your period cycle may not only lead to irregular cycles, but it could completely halt your menstrual cycle. This is because stress releases cortisol the stress hormone that could interact with the hormones responsible for the different phases of your menstrual cycle causing it to stop producing the hormones that initiate the menstrual cycle. 

This could be psychological stress on a daily basis, physical stress, or even emotional stress. When these chronic amounts of stress affect your cycle length, it could lead to a change in period dates, with symptoms during this cycle.

You might have symptoms like painful periods, nausea, bloating, breast tenderness, and weight. High levels of stress can even stop ovulation and menstruation altogether. This is called functional hypothalamic amenorrhea where cortisol communicates with the hypothalamus to put the menstrual cycle on pause. 

This could also happen when you exercise beyond your limit or overexercise. This is just a way your body protects you, especially times when your body might not be prepared to support a healthy pregnancy.

2. Pregnancy and Childbirth

Pregnancy is one of the most common causes. As long as you are sexually active, it is important you have an at-home pregnancy test. This is for you to always play safe. 

Irregular or no periods are commonly associated with pregnancy and childbirth, unless proven otherwise after tests. Until you know for sure whether you’re pregnant or not, you should treat yourself as though you are, by going to the doctor and midwives for confirmation to determine how far along you are, in addition to informing you on what else you should be doing for a healthy pregnancy.

However, if you're not sexually active and your period date fluctuates beyond its normal range, it is advised that you see a doctor. 

3. Date Alterations

Period dates vary from month to month. You might be wondering how, but here is the thing: The time between the first day of your last period and the first day of your next one is either less than 24 days or more than 38 days. 

For instance, if you get your period on the first day of the month, you are likely to get your period toward the end of that month, depending on your cycle, and how many days the month is made of, 30 or 31. It is possible that, from getting your period at the beginning of every month, you start getting it at the end of the month; it's just your cycle working and the days going by. 

Sometimes, your cycle length changes by more than 20 days each month, and it could be considered  irregular. Bear in mind that irregular periods could also be called “normal”, mostly during the first few years of menstruation and during perimenopause, the time leading up to menopause. 

4. Hormone Changes or Imbalances Due to Contraceptive Pills

When your estrogen level starts to fluctuate, it can alter your menstrual cycle, causing a change in period dates. This is very common in women in perimenopause (some women experience symptoms earlier. Possibly years before menopause), causing irregular or missed periods. 

Side effects of hormonal birth control could also be a factor.  They contain estrogen and progestin or progestin only. These hormones alter your menstrual cycle. Your period might come earlier or later than usual when you start hormonal birth control. 

You might also experience symptoms like sore breasts, hair loss, vaginal dryness or pain with intercourse, weight gain, hot flashes or night sweats, growth of facial hair, and skin tags, due to hormonal imbalances.

5. Medical Conditions

Common medical conditions like polycystic ovary syndrome (PCOS), endometriosis, and hypothyroidism affect your menstrual cycle, leading to irregularities. 

PCOS is a hormone imbalance that can affect ovulation and periods, making pregnancy difficult. 

Endometriosis is a condition where uterine lining tissue grows where it shouldn't,  like outside the uterus, in places like the ovaries and fallopian tubes. As your uterine lining thickens and sheds throughout your cycle, so does the lining tissue outside the uterus, which can cause an array of symptoms, including early periods and other menstrual irregularities. 

Hypothyroidism, also known as underactive thyroid disease, is caused when the thyroid gland does not produce enough of its hormone. This is quite similar to PCOS.

These conditions could be the reason your period dates fluctuate. You are advised to visit your doctor if the irregularity persists. If your doctor determines the cause of the changes, treatment may include birth control pills or other hormones to restore hormonal balance.

6. Lifestyle Changes

Some external or environmental changes may also cause fluctuations in your menstrual cycle. Changes like:

  • Excessive weight loss or gain. Low body weight and Obesity are common causes of missed or irregular periods. 
  • Strenuous exercise. Missed or irregular periods are common in athletes. 
  • Birth control methods, which may cause lighter, less frequent, more frequent, or skipped periods or no periods at all.
  • Pregnancy and breastfeeding. Most women do not resume regular periods until after completing breastfeeding.

7. Menopause

Your menstrual cycle is likely to change before you reach menopause. This is frequently linked to age. In your 30s, you're likely to experience age-related menstrual changes. This could result in shorter or longer, lighter or heavier periods, with more or less time in between.

Ways You Can Maintain a Regular Cycle

Your period might not fall on the exact days but within the range of your cycle. These are some ways you can maintain a constant cycle:

  1. Charting. Your menstrual cycle calendar is peculiar to you and it helps you track your period days.
  2. Try to maintain an ideal weight.
  3. Reduce stress. Find time to rest.
  4. Exercise often, but avoid strenuous ones.
  5. Try medication that helps with pregnancy and fertility; and if you're not trying to get pregnant, avoid self-prescribed contraceptive pills.
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