Birth control pills are 99 percent effective at preventing pregnancy when used consistently and correctly. If you do not use the birth control pill consistently (every day), or correctly (about the same time of day), your birth control pill's effectiveness is decreased.
How much are my pills' effectiveness decreased?
It is impossible to provide an exact percentage, but the basic formula is: the more pills you miss + (plus) the more frequent intercourse you have = (equals) the greater chances of pregnancy.
Why can't I miss a few pills if I've taken them for years? Is it a big deal if I miss more than one pill?
Yes, if you miss more than one pill it is a big deal, as each cycle counts as its own, and makes your pill-taking history irrelevant, as your body requires a consistent supply of the synthetic hormones to work effectively for each cycle alone. Every individual cycle presents an opportunity for ovulation, and this presents the opportunity for pregnancy. It is helpful to understand the basic mechanism of hormonal contraception in your body, as it works in one (or all) of these ways:
The pill essentially stops your body from these natural functions by way of introducing synthetic hormones into your body, resulting in your body's decreased production of its own natural hormones. Without the pill, your natural hormones work throughout your cycle to begin maturing an egg, release the egg (ovulation), and otherwise make a cozy environment for the sperm to enter and a fertilized egg to implant in the uterus. These processes are working continuously from cycle to cycle, and the birth control pills work to deter these processes on a daily basis. If any of these processes are given the ability to begin (due to forgetting to take a pill), you can see that it would give sperm the opportunity to enter your cervix, give your body the opportunity to ovulate, and this is why a pregnancy may occur if pills are not taken as directed.
What can I do now?
You may take a home pregnancy test (HPT) when your normally-expected period has not begun (any earlier, and the test will not be as accurate). It takes at least 10-14 days to become pregnant, and is the reason a HPT is not effective immediately after unprotected sex. Just as your cycle consists of many processes, so does the conception process. We wish we could tell you differently, but women must wait these two weeks after sex before taking a HPT. We understand this is a very long two weeks, and please know that no amount of worrying or wondering about symptoms will help these two weeks pass by quicker. Many women have found this time helpful by planning activities to get their mind off of the waiting; to write the “two week mark” on a calendar, so they can prevent themselves from dwelling on wondering if they are pregnant or not. Hang in there!
The simple solution?
If you miss pills (don't worry, we all do), simply choose to use a back-up method of birth control (such as a condom), or, choose to engage in other physically intimate sexual acts that do not include intercourse (penis-to-vagina sex, specifically). In the “heat of the moment”, this is a simple solution, but understandably not always easy. However, by preparing for the inevitable you can be in control of protecting your body, mind and spirit from the stress of a late period or unwanted pregnancy.
You may find related information on How to Make up Missed Birth Control Pills that details how to “double up” on your pills if you have missed one, two, or three pills.