Does Plan B Work During Ovulation? No, and Here's Why

Plan B is emergency contraception people use for pregnancy prevention. You can take this morning-after pill after having unprotected sex to lower your chances of becoming pregnant. However, one factor that may impact Plan B’s effectiveness is ovulation. Learn more about how ovulation can affect this emergency contraceptive pill.

What is Plan B, and how does it work?

Plan B is an emergency contraceptive method that helps prevent pregnancy within 72 hours of unprotected sex. According to the U.S. Food and Drug Administration (FDA), Plan B works by stopping or delaying the release of an egg from the ovaries. The emergency contraceptive pill is one tablet containing a higher dose of levonorgestrel than birth control pills.


Levonorgestrel, or the morning-after pill, is a synthetic hormone that is the first-line treatment for emergency pregnancy prevention. The hormonal contraception has also been used off-label to treat medical conditions like endometrial hyperplasia, menorrhagia, endometriosis, and menopausal hormone therapy.

When taken before ovulation, the emergency contraceptive can lower the chances of pregnancy by 75–89% if taken within three days of unprotected sex.

This emergency contraceptive is often seen as a backup after unprotected sex or when other methods of contraception have failed, such as broken condom or missed oral contraceptive pills.

Plan B is available over the counter at most pharmacies, so no prescription is required.

Does Plan B work during ovulation?

Plan B is not effective for preventing pregnancy during ovulation. This is because the pill is designed to delay ovulation. If you’re already ovulating, Plan B or any other emergency contraceptive pill will have already failed before it has a chance to start working in your body.

Once your egg is released from your ovary, sperm can reach it more easily to start implantation in your uterus lining. Implantation indicates that pregnancy has started.

If you are already pregnant, the FDA says that Plan B is not abortifacient. This means that the medication will not affect the pregnancy or cause an abortion.

How to know when you are ovulating


Knowing when you’re ovulating can help with choosing the best timing for emergency contraception.

Ovulation is a phase in the menstrual cycle in which an egg matures within one of your ovaries. Your ovary then releases the matured egg, allowing it to enter the fallopian tube to wait for sperm and the uterus. The lining in your uterus is thickened to prepare for the fertilized egg.

If a child is not conceived during ovulation, your uterine lining and blood will be shed, leading to menstruation.

A few signs and symptoms can alert you that you’re ovulating. These include:

  • Changes in cervical fluid. Your cervical fluid is an egg-white-like substance that indicates you’re near or ovulating. The amount and the look of cervical fluid or mucus differs for everyone. Ovulation typically takes place when you’re releasing a larger amount of cervical fluid.
  • Changes in basal body temperature. Your basal body temperature can change before ovulation, which is seen as a slight decline, followed by a sharp increase post-ovulation. This temperature change indicates that ovulation has occurred.
  • Changes in cervix position or firmness. As you ovulate, your cervix undergoes several changes. Your cervix can become wet, open, soft, and high during ovulation.

There are also secondary symptoms that may not occur every time you ovulate. These symptoms include the following:

  • Light spotting
  • Increased libido (sex drive)
  • Bloating
  • Breast tenderness
  • Cramping
  • Heightened sense of smell, taste, or vision

These symptoms can vary from person to person, and, in some cases, you may not experience any symptoms during ovulation. The timing of ovulation also can vary. You may ovulate on the same day of every menstrual cycle or have different start days each month.

How to track ovulation to prevent pregnancy

You can learn to track your ovulation to ensure you don’t take Plan B during your fertile window.


Below are fertility awareness-based methods of family planning for tracking ovulation:

  1. Rhythm method. This form of natural family planning involves determining your fertile window by counting the days from the start of your menstrual period each month. During this period, you may refrain from sexual intercourse or use another contraceptive method.
  2. Checking your basal body temperature. This method involves taking your temperature each day and charting it throughout your menstrual cycle to determine when you’re ovulating.
  3. Cervical mucus method. With this method, you’ll examine your cervical mucus to see any changes in its look and consistency. Cervical mucus tends to increase before ovulation, becoming thin and slippery. After ovulation, the mucus becomes thicker and less noticeable.

Another method you can consider is ovulation kits. Ovulation kits and tests can help you determine when you ovulate by detecting any rise in luteinizing hormone (LH) levels in your urine. A rise in your LH levels tells your ovary to release an egg.

If you decide to use these methods to prevent pregnancy, be sure to use barrier method contraception (e.g., condoms) to avoid STDs. Fertility awareness-based methods do not protect you against sexually transmitted diseases (STDs), such as chlamydia, syphilis, gonorrhea, or human immunodeficiency virus (HIV).

Alternatives to Plan B

There are two other emergency contraception options you can consider for preventing pregnancy.

Here are Plan B alternatives to consider:

Ulipristal acetate (EllaOne)

Sold under the brand name EllaOne, ulipristal acetate is another morning-after pill that prevents pregnancy. The pill can be taken up to 120 hours or 5 days after unprotected sexual intercourse.

The rates of pregnancy associated with Plan B and EllaOne are 2.2% and 1.3%.


EllaOne is unavailable over the counter and must be prescribed by your healthcare provider.

Copper IUD

A copper-containing intrauterine device (IUD) is another form of emergency contraception that is inserted into your uterus. While the copper IUD is approved for contraceptive use for up to 10 years, it is also used off-label for emergency contraception.

You can get a copper IUD inserted within five days of unprotected sex to prevent pregnancy. A copper IUD's failure rate after placement is about 0.1%.

Plan B is a popular emergency contraceptive many use to prevent pregnancy. However, if you’re already ovulating, this morning-after pill won’t stop the fertilization of an egg. To increase the effectiveness of Plan B, you can track your ovulation with natural methods or a kit and take it as soon as possible after unprotected sex. Or, you can consider other emergency contraceptives with lower failure rates, such as the copper IUD.

You can speak with your primary care physician or gynecologist to find the best emergency contraception options.


Key takeaways:
12 resources


Leave a reply

Your email will not be published. All fields are required.