The first and perhaps most common reason is testing a bit too early. You may have tested before your period was due because you couldn't resist the temptation any longer, you may have irregular periods and not know exactly when the next should turn up, or you could have miscalculated the date. It is also possible that you drank a lot of clear fluids, and your pee has become so diluted that the pregnancy test is picking up lower levels of hCG. Finally, some pregnancy tests are more sensitive than others. If this happens to you, we would advise that you wait a few days and test again. HCG levels double every few days during the first stages of pregnancy, and you are more likely to get a clearer result later on. This is especially true for early testers, and there are many of us! Still, if you managed to get a faint line, it is pretty safe to assume that you are indeed pregnant!