Medically reviewed by Sophia Yen, MD, MPH – Written by Pandia Health Editorial Team. Updated on January 25th, 2021

Math and birth control… an unlikely combination. Yet there is comfort in understanding the numbers. Let’s take a closer look.

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How do I calculate how effective my birth control is?

Do you ever wonder how you can really decrease your chance of pregnancy using birth control and how to calculate it? We have laid out the various types of birth control and how likely you are to get pregnant using each respective method.

Chances of getting pregnant while on birth control

Implant: Of the people with uteri that use the implant, 5/10,000 usually get pregnant giving you only a 0.05% chance of getting pregnant if you choose this method. (On its own, the most effective birth control option!) 

Hormonal IUD: On the IUD with hormone, 2/1000 women usually get pregnant. That means you have a 0.2% change of getting pregnant using this method.

Copper IUD: On the copper IUD , 8/1000 women usually get pregnant which means women using this method have a 0.8% of getting pregnant.

Birth control shot: Of the women that use the birth control shot, 6/100 get pregnant. If your means of contraception is a birth control shot, you have a 6% of getting pregnant.

Birth control ring: How effective is NuvaRing? On the birth control ring, 9/100 women (9%) usually get pregnant.

Birth control patch: Using the birth control patch, 9/100 women usually get pregnant (9%). This method has the same effectiveness (with typical use) as the birth control ring.

Combined birth control pill: On the birth control pill, 9/100 women usually get pregnant (9%).

Progestin-only birth control pill (POPs): When using Progestin Only Pills (POPs) , 9/100, or 9%, of women usually get pregnant.

Condoms for birth control: Using condoms, 18/100 women (18%) usually get pregnant. This method of contraception is the only way to prevent sexually transmitted diseases. To prevent STIs, condoms should be used in combination with another method, like the birth control patch.

Spermicide: With spermicide alone about 28/100, or 28%, of women will get pregnant.

*when used as directed. The math changes otherwise.

Birth control effectiveness math

Fearing pregnancy and childbirth is a very real thing. By combining multiple forms of birth control, the math is in your favor. If you really are afraid of pregnancy, I recommend these effective combinations with the lowest chances of pregnancy:

  • the implant + condoms combined = 9/100,000 or
  • IUD with hormone + condoms = 3.6/10,000.

Other common birth control combination math:

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Frequently Asked Questions

Is birth control 100 effective?

No. The only way to not become pregnant is to abstain from sex.

How effective are birth control and condoms?

The effectiveness of birth control depends on the method you choose. Condoms themself are 18% effective.

What are the odds of getting pregnant on birth control?

The odds of getting pregnant on birth control range from 0.05%-28%. It all depends on the type of birth control you choose.

How many people get pregnant on the pill?

Using the pill, about 9/100 (9%) of people get pregnant. 

How effective are birth control pills without pulling out?

Birth control pills are only 91% effective because people are not perfect—that is the effectiveness rate with typical use (people make mistakes!).

What are the chances of getting pregnant with an IUD?

Women using copper IUDs have a 0.8% chance of getting pregnant. Those using a hormonal IUD have a 0.2% chance of getting pregnant.

What are the chances of getting pregnant without protection?

Without any protection, you can be very likely to get pregnant. The chance of you getting pregnant without using any form of protection (e.g. birth control pills or condoms) is 85%. Keep in mind, if you don’t use a condom, you also risk sexually transmitted infections.

What happens if you get pregnant while on birth control?

It depends on which method you are using, but if it is the birth control pill, patch, ring, shot, or implant nothing would happen to the pregnancy. There have been several cases of women continuing to take their birth control until the day the baby was born (they didn’t know they were pregnant) and the baby was fine. 

If using an IUD, then there could be spontaneous abortion. Studies have shown that the risk of miscarriage, preterm birth, and infection of the amniotic sac and fluid before delivery (chorioamnionitis) is higher when IUDs are left in place during pregnancy compared to pregnancies in which the IUD is removed.

Why are condoms not 100 percent effective?

People are not perfect, which is why condoms are not 100% effective—this goes for other birth control methods too. Condoms can also fail as an effective method by breaking or being put on incorrectly.

The above information is for general informational purposes only and is NOT a substitute for professional medical advice. Always seek the advice of your doctor/primary care provider before starting or changing treatment.