Does Plan B Work During Ovulation? Effectiveness and Options

Medically Reviewed By Stacy A. Henigsman, DO

Plan B is a type of emergency contraception, also known as a morning-after pill. It works only when taken at certain times. For example, Plan B does not work during ovulation. Many people may use emergency contraception if they know or suspect they did not use contraception during sex or that the contraception may not have worked.

However, some factors can affect whether emergency contraceptive pills work. This includes where you are in your menstrual cycle when you take the pill and the type of hormone in the pill.

This article explains why Plan B does not work during ovulation and whether it is effective before and after ovulation. It also discusses how to know if you are ovulating, what to do if you have taken Plan B during ovulation, and when to contact a doctor, as well as alternative options to prevent pregnancy.

Does Plan B work during ovulation?

A person writes in a diary showing the days of the week.
Lucas Ottone/Stocksy United

Plan B does not work during ovulation. Other emergency contraception pills also do not work if ovulation has already started.

Ovulation is when an ovary releases an egg. This typically occurs once every menstrual cycle in people assigned female at birth. If you have sex without effectively using a condom or other barrier method, the released egg may join with any present sperm, leading to a pregnancy. 

Emergency contraception pills, such as Plan B, work by preventing this ovulation process so that no egg is available to meet any sperm that might be present.

However, if you have already begun ovulating for the month, it is too late for the pill to prevent ovulation. It cannot prevent sperm from joining the egg, which can live in the body for as many as 5 days Trusted Source Office on Women's Health Governmental authority Go to source .

If you plan on having sex, it is advisable to use another form of regular contraception rather than just relying on emergency contraceptive options.

Read more about contraceptive options.

Does Plan B work after ovulation?

The manufacturer of Plan B claims the pill will prevent fertilization if you have already ovulated. Alternatively, the manufacturer suggests that it may prevent a fertilized egg from attaching to the wall of your uterus. 

However, there is a lack of research to support the idea that Plan B is effective after ovulation.

Additionally, some other emergency contraceptive pills do not work after ovulation. In fact, some pills can only work before ovulation.

These pills include ellaOne, which contains ulipristal acetate, and Levonelle, which contains levonorgestrel. Levonorgestrel is also the hormone that Plan B uses, so some people speculate it may not work after ovulation, similar to Levonelle.

When does emergency contraception work?

Emergency contraceptive pills may work before ovulation.

Pregnancies are most likely Trusted Source Office on Women's Health Governmental authority Go to source to occur if you have sex without effective contraception from the 3 days before ovulation to ovulation.

Some pills are more effective immediately before ovulation than others. For example, pills that use levonorgestrel hormones, such as Plan B and Levonelle, may be less effective than ellaOne pills close to the time of ovulation.

Additionally, for emergency contraception pills to be effective, it is necessary to take them within 5 days of the sex without a barrier contraceptive. However, it is better to take them as soon as possible afterward for maximum effectiveness.

Planned Parenthood recommends using emergency contraception as soon as possible, even if you think you’re about to ovulate. This is because many people do not know exactly when they ovulate, and the pills may still take effect.

Learn more about how emergency contraceptive pills work, including Plan B.

How do I know if I’m ovulating?

Clinicians consider each menstrual cycle to begin on the first day of your period, ending before you have your next period. This time represents one cycle and is usually around 24–38 days Trusted Source Office on Women's Health Governmental authority Go to source .

Ovulation occurs during this cycle between periods. As each person’s cycle length differs, the time between ovulation and the following period may be between 7 and 19 days.

Because of this variation, knowing exactly when you are ovulating can be difficult. This is why Planned Parenthood recommends taking emergency contraception just in case you are not yet ovulating.

You may experience symptoms that indicate ovulation, such as:

  • slippery and clear vaginal discharge, that may resemble raw egg whites
  • minor cramping
  • slight rise in your basal body temperature, which is the temperature after sleeping and before you get out of bed

You may also be able to track your menstrual cycle and check for ovulation using methods such as:

  • taking over-the-counter (OTC) ovulation test strips
  • checking your basal body temperature every day and checking for any increases
  • recording your cycle on the calendar or in an app
  • checking your vaginal mucus

Read more about how to track your menstrual cycle, including ovulation.

What if I have already taken emergency contraception?

If you have taken emergency contraception but have already ovulated, the pill will not cause you any particular harm. However, you may still become pregnant.

There are other emergency contraceptive options you can try. Contact your doctor immediately for advice on options that may be effective for you.

When should I contact a doctor?

If you had sex without effective contraception, contact your doctor or pharmacist for advice on what options may be suitable for you.

This can include providing you with additional options if an emergency contraceptive pill such as Plan B will not work.

They can also provide advice on consistent birth control options to avoid having to rely on emergency contraception. Non-emergency birth control can be more effective.

Some people experience side effects due to emergency contraceptive pills. Mild side effects such as nausea or stomach pain are expected. However, if you vomit after taking an emergency contraceptive, contact your doctor to determine whether you should take another.

It is also advisable to reach out to your doctor any time you have questions or are unsure about your situation.

Learn more about the side effects of emergency contraceptives and when to contact a doctor.

How do I know if it worked?

After taking emergency contraception, it is advisable to take a pregnancy test to know whether it worked.

If you have been keeping track of your menstrual cycle, you may know when you are due for your next period and whether it is late. Some pregnancy tests may be able to detect pregnancy from the first day a period is late. However, others may need to test at least 21 days after sex for an accurate result, and results may be unreliable if you take them too early.

For more definite confirmation on whether you are pregnant, contact your doctor.

Read more about when to take a pregnancy test.

What alternative options do I have if Plan B does not work?

If you are already ovulating or have been advised that emergency contraceptive pills will not work, other forms of emergency contraceptives may help.

As with emergency contraceptive pills, these options do not terminate an existing pregnancy but can prevent the conception of a pregnancy.

Additional options include copper or hormonal intrauterine devices (IUDs). A clinician will place this device inside the uterus. While IUDs can also offer long-term, regular contraception, they may also be effective emergency contraception following sex.

In fact, copper IUDs, such as Paragard, can work up to 120 hours after having sex. They may also be the most effective type of emergency contraception. Hormonal IUDs such as Liletta also work up to 120 hours after having sex.

Termination of pregnancy

If emergency contraception does not work and conception still occurs, you may be able to terminate the pregnancy if you wish.

You have several options for terminating a pregnancy, including taking medication or having surgery.

Your doctor can advise you on what option may be the most suitable for you, as well as give you information on abortion access and legality in your state.

Learn more about options and access to abortion.


Emergency contraceptive pills such as Plan B do not work during or after ovulation. However, some experts suggest using emergency contraception anyway, just in case you are not yet ovulating.

Other emergency contraceptive options may still help. These can include a copper or hormonal IUD, which may work up to 120 hours after sex without effective contraception.

You can check whether you’re ovulating using OTC tests. It is also advisable to keep a record of your menstrual cycle and use regular, non-emergency contraception if you are sexually active and could get pregnant.

Contact your doctor for individualized advice regarding emergency and non-emergency contraception, and pregnancy.

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Medical Reviewer: Stacy A. Henigsman, DO
Last Review Date: 2022 Nov 30
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