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Cycle Basics: Why is my period late?

Updated: Aug 4, 2018

Ah yes, the Late Period, perhaps the greatest source of worry and confusion for we menstruators! Let's check out some reasons for why your period might be late.

First of all, what defines a late period?

I often hear folks say that their period was late just because it didn't come exactly 1 month after their last. I'm here to tell you that it's considered normal to have cycle lengths that fluctuate between approximately 24 – 36 days (meaning your period comes between every 24 – 36 days). If you usually get your period on the 1st of every month, for example, you don't need to consider it late if it still hasn't started by the 3rd, or 5th, or even 8th. That's because it's totally normal for there to be some variation in your cycle lengths.

“Irregular” periods mean that there is great variation from one cycle to the next, for example, a period that comes on May 5th and doesn't come again until June 20th. When your period is several days early or late, that doesn't mean you have irregular periods.

So why do cycle lengths fluctuate? They fluctuate not because they're random and unpredictable, but because the timing of ovulation varies cycle to cycle.

Ovulation is the whole reason we have cycles at all. If we didn't ovulate, we wouldn't have periods!

We have to ovulate first before we can menstruate, and the body doesn't ovulate on the same day every cycle. Sometimes it may be on day 12 of the cycle, and the next month, it may be on day 20. Because menstruation comes approximately 2 weeks after ovulation, the day you start your period depends on when you ovulated. Say you usually ovulate around day 15 of your cycle, but this month, your body didn't release an egg until day 22. You wouldn't start your period until 2 weeks later – around cycle day 36 – and you'd be wondering why your period was so late.

It really helps to know that ovulation is the key event driving the cycle, and until you ovulate, you won't start your period (it will come about 2 weeks after ovulation).

Late ovulation is the real reason for your late period.

Here are some reasons why ovulation – and therefore, your period – may be delayed:

1. Stress

You knew I was going to say this, right? Let me explain why stress is so detrimental to having consistent ovulation (and in turn, good hormonal health and periods that come on time). The body makes our cycle hormones, estrogen and progesterone, from the same substances that are used to make stress hormones. If we're faced with a fight or flight situation, do you think the body will prioritize making reproductive hormones or stress hormones? It chooses to make stress hormones so that we can survive through times of hardship and conflict. These days, that may not mean running from wild animals or surviving famine; it means chronic stress at work, at home, in a relationship, or stress caused by diet and lifestyle. Every time we feel stress, the body robs those chemical compounds that would normally go to making our cycle hormones and uses them to make cortisol and adrenaline. The body struggles to make estrogen and progesterone, which throws off our ovulation.

2. Diet

Our bodies make estrogen and progesterone from cholesterol, most of which we obtain from food. If your diet contains little to no cholesterol or saturated fats, your body will have a harder time making healthy hormones and producing regular cycles. Fasting or doing a detox may also decrease the strength of your hormonal activity.

3. Lifestyle

Perhaps you've experienced a life change: your wedding is coming up, you just moved in with a partner, you've started a rigorous new exercise program, you left a relationship, there was a big earthquake, you had to fire someone at work, your daughter left for college, etc. All of these things represent a form of stress – positive or negative – that may delay ovulation, thereby delaying your period.

4. Being underweight or overweight

Regular cycles depend on good hormone balance. If the body has a deficit or an excess of body fat, hormones can't do their job as well. Ovulation may be delayed or nonexistent, meaning late or very irregular periods.

5. An underlying health issue

Our cycles don't exist in a vacuum. In fact, our cycles are "downstream" from all other body systems and whatever happens "upstream" will impact our hormonal health. Late periods can be a side effect of a thyroid or adrenal issue, polycystic ovary syndrome, diabetes, celiac disease, or anything else that's upsetting your health.

After you ovulate, though, none of these things will delay your period. If ovulation is delayed, then obviously your period will be delayed, too, but there's no way that stress, diet, or life changes will actually make your cycle lengthen on its own after ovulation. If anything, those things may actually shorten your cycle after ovulation due to stress hormones stealing the precursor needed to make progesterone, which is the dominant hormone after ovulation.

You'll notice I didn't mention pregnancy. It's a pretty obvious possibility, but here's something I bet you hadn't heard before: if your post-ovulatory phase is 18 days or more – usually it can be no longer than 16 – you're almost certainly pregnant! If you practice Fertility Awareness, you can see this on a chart very easily because your waking temperature will be high 18 days in a row.

Speaking of which, a wonderful way to know exactly why your periods seem to be late is by charting your cycles with Fertility Awareness. This is an easy daily practice that involves observing 2 signs of fertility and writing your findings on a special chart. You'll be able to see when and if you ovulate, the health of your hormones, the day your period will come, if you're pregnant, and much much more.

At the end of the day, though, your late period is probably nothing to worry about. Remember that our bodies are not machines and we may ovulate later in certain cycles, meaning our period will come later as well.

If you consistently have cycles that irregular, such as 30 days one month and 45 the next, it would be worth looking into what's going on.

Still have questions about late periods? Want to suggest a topic for my next Cycle Basics post? Let me know in the comments below.

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