It is common to mistake perimenopause for menopause and vice versa.  Labs can be misleading. Doctors can be misleading in your concerns about whether you are in perimenopause vs. menopause.  Even symptoms can be misleading. In this article, I am going to explain the differences between perimenopause and menopause.  As well as information to help you determine which hormone phase you are in at the moment.
Both perimenopause and menopause can start between 35 to 50years old.  As the word states, perimenopause starts before menopause. While that might seem obvious, sometimes it is hard to differentiate between them.  I have had many patients tell me they are in menopause but are really in perimenopause. You might be asking, ‘why is it a big deal to know the difference?’.  That can come down to the treatment. Treating a woman for menopausal symptoms when she is in perimenopause can not only be ineffective. But can make the symptoms worse as well as new symptoms.
Perimenopause usually starts in the mid-’40s, but I have seen it as early as the early ’30s.  The average age of menopause is 51 years old, but I have often seen it occur in the mid-’40s. So while it seems that perimenopause and menopause can overlap, there are distinctions in the symptoms.
Some distinctions between perimenopause and menopause: I will try to be as comprehensive as possible. Here are the most common differences in symptomatology between perimenopause and menopause.
Periods:
In perimenopause, if you still have your uterus, then you will be having a period.  The periods can change from your “normal.” But you will still be having a regular period.  What you might notice are periods might be heavier, longer, more spotting, more cramping. Often this can lead to low-iron/anemia.  
This is the time that women find out that they have fibroid(s).  Fibroids are benign growths in the uterus and during perimenopause can become “active,” causing cramping, heavier periods and more spotting.  This is usually the time women will get a hysterectomy. The periods are so “off” that most doctors only recommend a hysterectomy. Now that might correct the period “issues.”  But it does nothing for the other symptoms.    
In menopause, the periods become less frequent.  Might miss one or many months at a time. The period that you do have can come at any time. They might be light one month and then four months later a heavy, painful period.  
Hot Flashes and Night Sweats:
In menopause, you will have lots of hot flashes and night sweats.  But the distinction here is, in perimenopause you don’t have daytime hot flashes. But you will have night sweats, really bad night sweats.  The night sweats in perimenopause usually happen anywhere from 7 to 10 days before your period. But once you get your period, the night sweats go away.  
Mood: 
In perimenopause, you are much more irritable than in menopause.  That is one of the most common complaints in perimenopause. Short-fuse, low tolerance, very little patience for even minor offenses.  The impatience and overwhelmed wound up feeling is not seen as much in menopause as it is in perimenopause.