Can You Get Pregnant on Birth Control?

Medically Reviewed by Murtaza Cassoobhoy, MD on March 12, 2023
9 min read

It’s happened to a lot of people – maybe even you. You get busy and forget to take your birth control pill. The moment you realize it can be scary, but it doesn’t always mean you’ll get pregnant.

Birth control pills don’t prevent pregnancy 100% of the time. But they come close when taken as directed.

Because no method of birth control is guaranteed, and because it’s so easy to make mistakes, it’s important to understand what birth control pills and other types of birth control do -- and how you can make them more likely to work.

Birth control pills come close to being 100% effective if you take them perfectly, meaning at the same time each and every day. If you don't, your odds of becoming pregnant go up to 9%.

There are different types of birth control pills, including combined pills and mini-pills. No matter which kind you use, it’s important to take them exactly as prescribed, even on days you don’t have sex.

Combined pills contain two hormones, estrogen and progestin. A pack of combined pills usually has 21 to 24 days of hormones and 4 to 7 days of reminder pills, although there are some with 26-day active pills. You should get your period while taking the reminder pills. It is important to take all pills in the pack, including reminder/inactive pills, to make sure no active pills are missed.

You might take one pack of combined pills every month, or you can take the hormone pills continuously to delay or stop your periods. It’s generally considered safe to skip or eliminate your periods, but you should discuss this option with your doctor and then follow their instructions on when to take the pill.

Mini-pill packs contain only one hormone, progestin. If you’re taking mini-pills, it’s very important to take all 28 pills at the exact same time every day. If you’re late taking a pill by just 3 hours, you have to use a backup method of birth control, such as a condom.

The pill doesn’t start working right away. You need to take it for at least a few days before it becomes effective. That’s why it’s important to use a backup contraceptive, like condoms, when you first start taking it. 

Talk to your doctor about how long you need to use a backup method. Some recommend you use one during your entire first pack.

Also talk to your doctor if you just had a baby or you’re breastfeeding and want to take the birth control pill. You may have to wait for a certain period of time before it’s safe to start on the pill.

Remember, the pill doesn’t protect you against HIV or other sexually transmitted diseases, so you need to continue to use condoms every time you have sex, especially with new partners, to stay safe.

You should take all your pills as directed, no matter what. Skipping a pill for any reason can increase your chances of becoming pregnant. If you’re tempted to skip a pill because they are causing side effects, talk to your doctor but continue taking them. Many women who have side effects when they first start taking the pill feel better after 3 months.

If you miss one pill, there’s probably no need to worry. Just take it as soon as you remember and continue taking your next pill at the regular time. If it’s a mini-pill and it’s been more than 3 hours, use a backup method of contraception.

If you’re taking combined pills and miss two or more hormone pills, you should call your doctor. What you should do next will depend on what kind of pill you’re on, so they can advise you. No matter what, you should use a backup method of birth control, like a condom, since your chances of getting pregnant are much higher after you miss two or more pills.

Whether or not it’s a great idea, alcohol and sex often go together. Drinking alcohol won’t change how well your birth control pills work. But, because effective use of the pill relies on memory, you’ll need to think ahead when drinking is in your future.

Alcohol can cause issues in judgment and alters your behavior. It can make you more careless – and derail your intentions to use birth control pills responsibly. A study of binge drinking in young women found risky drinking nearly doubled the odds of contraception not working well.

Drinking too much can also make you throw up. If you throw up after taking the pill less than 2 hours prior, it can come back up, and then it's as if you never took it at all.

Oral contraceptives can also affect how your body processes alcohol. Like some other drugs, birth control pills slow down the rate at which your body absorbs it, making it linger longer. And the longer you're under the influence, the more time there is to forget to take your pill, too.

If you plan to drink alcohol, the way to stay on track with your birth control is to plan ahead.

  • Use reminder apps. You can find a wide variety of these with a web search. Many can track your period and even your pill inventory.
  • Take your pill early in the day instead of the evening, when impromptu events might come up.
  • Carry backup protection such as a condom and spermicide. Ask your partner to support your efforts and do the same. You should always use condoms to protect against sexually transmitted infections (STIs) unless you're in a long-term, faithful relationship.

Even if you take them as directed, there are some reasons your birth control pills might not work. These include:

  • You’re vomiting or have diarrhea for more than 48 hours.
  • You take the antibiotic rifampin, the antifungal griseofulvin, certain anti-seizure meds, or the herbal supplement St. John’s wort.
  • You’re obese. Some research suggests that the birth control pill doesn’t work as well in very overweight women.

If you have any of these issues, talk to your doctor about using condoms as a backup method, or switch to another form of birth control entirely.

Patches and rings. These work similarly to the birth control pill. You either insert a ring into your vagina (Annovera, NuvaRing) or place a patch on your belly, upper arm, buttocks, or back (Ortho Evra). Like the pill, they’re over 99% effective when you take them exactly as you should. But if you don’t, they’re only 91% effective. 

They can fail because:

  • You don’t put a new one in on time every month, or it’s out of your vagina for more than the recommended time. The patch can’t do its job if it falls off or if you don’t put a new one on at the right time every week.
  • You take certain meds. The same drugs and supplements that make the pill less reliable also affect the ring and patch the same way.
  • You’re carrying extra weight. Research has found that the patch doesn’t work as well for women who weigh over 200 pounds.

If you use one of these methods, and it falls off or you forget to change it in time, reinsert or replace it within 48 hours. (If it’s been more than the recommended time, use a backup method for the next 7 days.)

Birth control shot. You get Depo-Provera, or the birth control shot, every 3 months. It contains the hormone progestin, which stops ovulation. Typical use is 94% effective because people don’t always get the shot on time.

It’s important to get your follow-up shots within 10 to 15 weeks after your last one. If you wait longer than that, you’ll need to use a backup method of birth control for a week.

Birth control implant. This is a thin, matchstick-size rod that your doctor inserts into your arm. It releases hormones that prevent pregnancy for up to 3 years. It’s virtually foolproof, since it’s already in your body and you don’t have to remember to take it or to use it the right way. As a result, it is over 99.9% effective for both typical use and perfect use.

But if you’ve had it for 3 years and you still don’t want to get pregnant, you have to replace it. Otherwise you could end up with an unexpected pregnancy.

IUDs. Your doctor inserts this into your vagina to prevent sperm from reaching an egg. It’s more than 99% effective whether you use it perfectly or not. Unlike other forms of birth control, you can’t forget to take it or use it the wrong way. 

Once it’s in, you’re protected from pregnancy for anywhere from 3 to 10 years. There are two types of IUDs: copper (ParaGard) and hormonal (Kyleena, Liletta, Mirena, and Skyla).

But if you do get pregnant, it’s usually because your IUD has slipped partly or completely out of your uterus. If this happens, see your doctor right away. 

With IUDs, there’s a higher risk of life-threatening complications such as ectopic pregnancy. That’s when an egg implants outside of your uterus. You’ll need to get checked for this. Even if your pregnancy is in the right place (your uterus), your doctor will still need to try to remove your IUD. That’s because there’s an increased risk of miscarriage if it’s left in place.

Vaginal contraception. This is inserted into your vagina before you have sex to create a hostile environment for sperm, so they won’t reach your egg for fertilization. This type of birth control comes in several forms including foam, jelly, tablet, cream, suppository, or dissolvable film. 

Normally, during sex, your vagina’s pH level rises to allow sperm to move toward your reproductive canal. Spermicides contain chemicals that kill the sperm before they make their journey. A new prescription nonhormonal gel called Phexxi keeps the pH level of your vagina at its normally acidic level, causing sperm to die without progressing.

Each of these methods has to be used before sex, and given time to be effective (usually 15 minutes). If used properly, spermicides are 70%-80% effective but work better when you combine them with a condom or diaphragm. Phexxi is considered 86% effective when used correctly.

Barrier methods. Like the diaphragm, cervical cap, or male or female condom, these methods physically block sperm from entering your uterus. They’re much less reliable than hormonal methods of birth control. 

The male condom, for example, is 98% effective with perfect use, but only 82% otherwise. That means 18 women out of 100 who regularly use condoms with their partner will end up pregnant within a year. Condoms often break or aren’t put on correctly.

Barrier methods work better if you pair them with spermicide, a type of birth control with chemicals that stop sperm from reaching an egg.

Fertility awareness methods (FAMs). Also called “natural family planning” and the “rhythm method,” these help you track your menstrual cycle so that you know when you’re ovulating. To do this, take your temperature every day, check your cervical mucus, or chart your cycle on a calendar. 

If you use at least one of these methods, and you follow it perfectly, there’s less than a 5% chance you’ll get pregnant. But that can be tough for most people, which is why the typical effectiveness rate hovers around 76%.

If you use multiple FAMs together, they’re more likely to work. But this isn’t a good option if you have irregular menstrual cycles.

If you miss a period, take a pregnancy test to make sure you’re not pregnant. Other signs include tiredness, bloating, having to pee a lot, moodiness, nausea, and tender, swollen breasts. Most pregnancy tests will be positive by the time you miss your first period.  But even if yours isn’t, it’s still important to see your doctor if you’re more than a week or two late. That’s to rule out any other health conditions and to confirm that you aren’t pregnant.