How long is too long for a delayed period before one should take a pregnancy test?
The most accurate day to test is 1 day after your expected period start date, but, you can try a test up to 4-5 days before your period is due.
After the egg is fertilized, it travels to the uterus (womb) and implants itself in the uterine wall. At this stage, tiny amounts of the pregnancy hormone, hCG, start to appear in your urine. Home pregnancy tests use this hormone to detect a pregnancy and some tests are so sensitive that they can be used up to 6 days before your missed period (which is 5 days before your expected period).
So, for example, if you expect your period on the 15th of the month, you can test as early as the 10th. However, if you are testing early, you should be aware that even if your result is not pregnant, you may still be pregnant. This is because levels of hCG vary from person to person and there may not yet be enough hormone for the test to give a positive result. hCG levels rise rapidly in early pregnancy, meaning that if you test again on the day of your expected period, your result (whether positive or negative) will be over 99% accurate.