The fact that you are even asking this question is good in one way: You know that you are not fertile for your entire cycle. Hooray!

I’m going to let you in on one of the few things that I “learned” about periods and menstrual cycles (before I learned anything about fertility awareness).

I was in college. Anatomy and physiology (actually one of my favorite courses in college). My professor was a fucking cool chick, but she decided to tell us a “fact” that certainly stuck in my head, and probably stuck in the head of my class-mates, too. Not only that, but they probably haven’t gone on to learn more about it like I did (boo for them).

That fact? She told us it’s impossible to get pregnant from having sex on your period. There were some other things she threw in there, and I can’t even remember everything. But the period sex thing, well that was worth remembering.

I mean, awesome, right? A fail-proof way to know a piece of your cycle that you are absolutely not fertile. Killer.


But here is the problem, that advice is not totally correct.


When I am talking about this you should keep a couple of things in mind. One is that bleeding does not necessarily equal period, though it’s perceived that way by most people.

A true period comes 12-16 days (generally) after ovulation and is the result of a steep drop in hormone levels because of something called the corpus luteum that only has a certain number of days it can stay alive. The corpus luteum is formed during and after ovulation.

But there are other times that bleeding may happen and it’s considered a period, even though it is not. One of the most common is when women are on hormonal contraceptives. Most hormonal contraceptives cause you to stop ovulating (at least most of the time), so the bleeds you have are not true periods.

Other times that you can bleed and it not be a true period are when you have a bleed within an anovulatory cycle (meaning you didn’t ovulate), you can spot while ovulating, and there can be other times of bleeding that are not periods and not regular healthy events.


So first, all of these non-period bleeding events can be mistaken for a period when you are not charting your cycle.  Especially if you are spotting during ovulation, your period would not be a safe time.


What else? If you KNOW that your period is just that, a period, is it then safe to have unprotected intercourse and not have to worry about getting pregnant?

While your period is often an infertile time, and when you learn how to use the sympto-thermal method of fertility awareness you will certainly know whether you should use it as an infertile time or not, you NEVER want to assume that you are infertile just because you are on your period. Let’s explore why…


Generally, when on your period your cycle will be a bit like this:

period v. cervical fluid



So the number is the day of your cycle. The red is when you are on your period (I know, I am so creative, thank you), the blue is when you have cervical fluid (if you need a refresher, this is what helps keep the spermies alive until your egg is good and ready to get fertilized), and the arrow is when ovulation is happening.

For most people ovulation (and the cervical fluid that surrounds it) happens far enough away from the period that they will indeed not get pregnant from unprotected intercourse on their period. This example would be one of those people. But here is the deal, the picture can look different:

period v. cervical fluid(1)



In the above case, the woman has a very long period. Ten days. Some of those days at the end might just be spotting, but you can often not determine whether you have cervical fluid or not while spotting. You can see that in this example on day ten she has both blood and cervical fluid.

Another example:

period v. cervical fluid(2)



In this one the cycle is shorter because she ovulates earlier on in the cycle. Her period is a normal length, though. In this case the cervical fluid could have started on day 6 and she would not have known because she was still experiencing menstruation.

This is why it is so important to not just blindly believe that you won’t get pregnant on your period.

If you want to use any kind of birth control method that relies on knowing when you are fertile (and you don’t want to get pregnant) you NEED to understand cervical fluid. Do not just count days on a calendar. Do not just assume you are infertile because you are bleeding.

Should I say it again? Make sure that you are fully trained to know when you are actually fertile during your cycle if you are planning on using any kind of fertility awareness for birth control. The training should include through information about cervical fluid.

So have you heard that you can’t get pregnant from sex on your period? Did you know there was a little more nuance to it than just “When you bleed you aren’t fertile”?





  1. If you need a testimonial for this particular article, I have a 16-year old son I can introduce you to…. =) Haha….. he’s AWESOME and I wouldn’t change a thing about my past. I was in my late thirties when he was conceived. It’s not that I was oblivious to the fact that you can (and I did) become pregnant during my period. I did however, feel that I was in a ‘safe’ zone. Thank you for sharing this information. It’s very important and relevant.

  2. angela benson says:

    i love this