According to most packaging on store-bought tests, they are 99% accurate. However, the accuracy depends on how well you follow the instructions. Timing is everything also, if you test too soon you may not get accurate results. To determine how well pregnancy tests work we must look at how they work and the reasons behind the false readings. How Do Pregnancy Tests Work  There are two types of pregnancy tests, blood tests, and urine tests. Blood tests are a little pricier and can only be done in a doctor’s office. Urine tests can be done in a doctor’s office and at home. There are some cases where a blood test is the better option, especially for those who have a history of pregnancy complications. When you become pregnant, your body produces something called human chorionic gonadotropin. It is released in your urine thus allowing urine tests detect HCG. Blood tests can detect HCG levels in the blood and will help determine Pregnancy 1 to 2 weeks earlier than most urine tests.  False Positive on a Pregnancy Test False positives can occur for a few reasons, one being that you have recently miscarried. This is because your urine still carries traces of HCG from your previous Pregnancy. A recent abortion within the last two months will also cause a false positive too. A chemical pregnancy is when a fertilized egg plants itself in your uterus but doesn’t develop, and you then end up getting your period a few days late. If you test before you get your period most likely, you will get a false positive. Finally, if you are taking a fertility drug that contains human chorionic gonadotropin the test will pick up the HCG and give a positive result. This is because this fertility drug contains human chorionic gonadotropin.  Pregnancy Test False Negative Result A false negative can be the result of testing too soon. Most tests recommend waiting until after you have missed a period. It is best you wait at least one day after your missed period. Although there are a few tests out there that claim results up to a week before your missed period, you will be better off waiting until that missed period to guarantee the best results. Some medications can also interfere with the tests. It’s best to get further testing especially if you are experiencing pregnancy symptoms or you feel pregnant.  So, are pregnancy tests accurate and how accurate are they? Pregnancy tests are accurate when used correctly, but many factors will lead to inaccurate results. If there are human chorionic gonadotropin levels in your urine, a test will pick it up. If there are other factors such as those that could lead to a false positive or negative, such as medication and complications, you will have to consider that when testing. Take note of any current medications including fertility drugs that could lead to a false reading. For best results test as soon as 1 to 5 days after your missed Period. If you are following directions accordingly, you should get the most accurate results from your pregnancy test.