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Delayed Periods! How Late Can My Period Be After Taking Plan B?

October 22, 2021

Home » Delayed Periods! How Late Can My Period Be After Taking Plan B?

How late can a period be after taking the morning after pill? The morning after pill is not the most effective method to use if you want to prevent pregnancy after unplanned sex. BUT – it is easy to get hold of compared to the other methods (like the Copper coil) and therefore, its the most common option for many people.

But after using the pill, a lot of practical questions come to light.

For instance, how to know if the pill worked and can the morning after pill make you miss a period.

Others are: does the morning after pill affect your period, or issues around the late period after morning after pill.

We will address these questions in detail in this post.

How The Emergency Contraception Pill Works

The EC pill is the method you reach for after having unplanned sex when you do not have protection. Protection means taking a regular contraception method like daily pills, implants, injections, or using a condom before sex.

Currently, after unprotected intercourse, we have two main methods for preventing an unplanned pregnancy – the emergency pills or the copper IUD.

The Copper IUD (intrauterine device) or Copper coil is a small device that an experienced health provider fits inside your womb in the clinic.

It is the most effective emergency birth control method and needs to be fitted within five days of unplanned sex or five days of ovulation. 

But if you can’t get the Copper coil, the emergency contraception pill is your next best bet.

how late can a period be on birth control

Emergency Contraception Pill Forms

EC pills come mainly in 3 different forms.

  1. The most common method is Levonorgestrel (LNG), an artificial progesterone similar to the Progesterone found in your body. It is what you find in the most familiar methods like Plan B, Take Action, Post pill, Postinor, and so on.
    • With Levonorgesterel, you have up to 72 hours of having unprotected sex in which to use the tablet. It is up to 95% in preventing pregnancy when taken within the first 24 hours. This reduces to about 89% by the 3rd day after sex. Thereafter, it is not reliable.
  2. The second form of emergency contraception pill known as Ella (EllaOne) contains the antiprogesterone, Ulipristal acetate. It is the most effective emergency pill method you can take (as long as it’s within five days of unprotected sex).
  3. Less commonly, some types of the combined pill can be used as emergency contraception. However, this is less effective than the Ella or LNG and not frequently recommended.

What The Pill Does…

The emergency pills work by delaying ovulation, that is, the release of an egg from the ovary.

  • In a woman with a regular 28-day cycle, the release of an egg usually happens about 14 days following the first day of the last menstrual period.
    • A regular cycle means you usually will have a montly bleeding about the same time each month with one or two days earlier or later on some occasion.
  • The day after ovulation, ovulation day and the four days just before ovulation are known as your fertile window.
  •  Your fertile window is the time of the month during which you are most likely to fall pregnant. But the timing of the fertile window can change from one month to the next, even in a woman who has a regular cycle.
  • Some studies suggest that more than 7 out of ten women may be in their FW before day ten or after day seventeen in their cycle.
  • Using a good ovulation app can help you keep track of your periods. You can also estimate your fertile window if you have a regular cycle.

The pill changes your hormones to prevent the release of the egg, usually till sperm from sexual activity have died off.

Since we know that sperm can remain alive in the woman for 3-5 days, the hEC pill delays ovulation for 5 days after which you then ovulate.

If you do have sex again after the postponed ovulation happens, you could get pregnant despite the pill. Hence you must resume your regular contraception method straight away or use another emergency pill after sex.

How late can a period be

Signs That Plan B Didnt Work

If you take an emergency pill like Plan B, you will need to wait till your next period or do a pregnancy test to know if the pill worked.

The urine pregnancy test will not be positive till around 2-3 weeks after intercourse.

Your next period may come about the same time or be delayed by the pill.

In some women, it even comes earlier than usual.

Whether you rely on your period or a pregnancy test, you will need to wait a few weeks before you can tell if the pill worked or not.

So – are there any signs that Plan B didn’t work? No – there’s no way we can tell. 

It would be best if you did not rely on spotting or breast soreness as signs the pill has worked or not without getting a test or speaking to your doctor.

How to make sure the EC pill works for you

However, there are ways you can boost the chance your pill works when you take it. 

  1. Take it as soon as possible after unprotected sex. If you are not ready for pregnancy, it is helpful to keep a dose of the EC pill at home in case your regular method fails. This reduces any delay in starting the pill.
  2. Where are you in your cycle? Knowing your fertile window (FW) tells you when you are safe.
    • The closer to ovulation you are, the more likely you are to fall pregnant after sex. When you take an EC pill after unprotected sex, it is most likely to work if it’s taken well before your ovulation day.
    • We think the pill is likely to be most effective if taken from the start of your FW till the day before ovulation. For the last two days, if ovulation has already taken place, the pill is unlikely to work.
  3. The type of EC pill you take. Ella has been shown to be more effective than the Levonorgestrel pill. It is also effective for 48 hours longer than the LNG.

Can the Morning After Pill Delay Your Period?

So you want to know how late can a period be without being pregnant. But can the emergency birth control pill delay your period? Yes.

The three potential effects of the pill on your period are:

  1. No effect – that means your period arrives on the same day as expected.
  2. Delay – the period arrives later than usual. Most often, this can be seven days or up to 2 weeks after the expected period.
    • However, some women report even longer delay after taking the EC pill when they are not pregnant. Sometimes this may be related to the pill – for instance, taking more than one pill in one cycle could mess up your periods for a while, but it should return to normal.
    • If this is not the case, your doctor will consider other causes.
      • Examples are:
        • weight changes (being over-or under-weight),
        • stress,
        • PCOS,
        • thyroid hormone problems,
        • anxiety or depression,
        • chronic illness, or
        • being in perimenopause and others.
  3. Early – In some women, your period may come on earlier than expected after the pill. According to some studies, taking the EC pill early in your cycle could mean the next period comes early. But this is not something we see all the time, so it’s not very reliable.
how late can a period be without being pregnant

How Long After Taking The Morning After Pill Should I Get My Period?

The answer to this will depend on a few factors.

  1. When in your cycle did you take the pill – early or late
  2. How many EC pills have you taken in this cycle 
  3. Are you taking regular contraception? 
  4. What was your cycle like before taking the pill?


It is not easy to predict this, but based on the studies, we know that a small number of women taking the Ella pill have their menses more than seven days early.

20% of them had a period delay of about seven days.

In about four women out of 100, their period delay was more than 20 days. This delay happens more often when they take Ella early in their cycle (before ovulation).


For LNG pills like Plan B or Postinor, most women get their periods within seven days of the expected date.

However, in about 10 per cent, it may be delayed over seven days.

Therefore on average, you should get your period within seven days of the expected date – but it is possible to have delays for more than two weeks.

Given this information, then, what is the maximum delay in periods after taking morning after pill?

We don’t know. Potentially this can be different from one woman to the next. However, with a period delay of over six weeks, your doctor will consider other possibilities apart from the emergency pill. 

If you are not pregnant, your doctor will check if this is related to your mental health, physical weight or other conditions that affect your hormones. 

So if we ask the question – can the morning after pill delay your period for 2 months?

Most doctors will say while this is possible; it is not common. They will recommend an examination and tests to check for other causes.

More FAQs on Delayed Periods After Morning After Pill

  1. Can the morning after pill mess up your cycle for months?      
    •  Yes, it can. Although it will not cause significant harm, taking the EC pill more than once in a cycle can mess up your cycle for months. And this is why we advise you to have a regular, reliable form of contraception, so you only need the morning after pill occasionally or rarely.
  2. What it means – morning after pill, period late 2 weeks? 
    • In this case, I would recommend a urine pregnancy test straight away. If the test is negative, you can wait another seven days and repeat it. At this point, you can also look for signs of early pregnancy like breast soreness, tiredness and so on.
  3. Bleeding a week after plan b – is that my period?
    • Most often, bleeding that happens soon after taking the pill is a side effect of the hormones in the pill – not your period. The bleeding also tends to be lighter than a period, e.g. spotting. Even if the bleeding is a little heavier, it will not cause blood clots. It will not last as long as a usual period. 
  4. What are the side effects of morning after pill on menstrual cycle/effects of morning after pills on periods?
    • The pill has two main bleeding effects: it can i) cause bleeding unrelated to the menstrual cycle (periods) and ii) affect the periods.
      • For the periods, the pill can have zero effect. That means the period is unchanged and comes at the expected time. In other cases, it may be delayed or might come earlier.
      • Some women have bleeding in between the scheduled period days. This could be the effect of the hormones from the pill. In addition, after taking an EC pill, you may experience less pain with the next period, and it may be less heavy than usual.  
  5. How late can a period be on birth control/ how many days late can a period be? If you want to know how long can a period be late after energency birth control pill – it varies. Yes it’s one of those questions you can’t predict. It may depend on different other circumstances like stress, or your natural period and using regular conteraception or not.

Hopefully, we’ve addressed the most common questions about period delays and other changes to the menstrual period after taking the emergency contraception pill.

Let us know in the comments if you have any more or ask here.

Editing by AskAwayHealth Team


All AskAwayHealth articles are written by practicing Medical Practitioners on a wide range of healthcare conditions to provide evidence-based guidance and to help promote quality healthcare. 

The advice in our material is not meant to replace the management of your specific condition by a qualified healthcare practitioner.
To discuss your condition, please contact a health practitioner or reach us directly through

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