Oops sorry... read the question wrong... its most accurate if you wait until you have missed your period... but you can test up to 5 days before depending on the test... but remember the accuracy of result only gets better the longer you wait... if you were to test to early (even within those 5 days you could get a false neg)
I would wait until you missed your period... if you possibly can... or if you don't know when your period is supposed to start then 14-19 days after you think you may have conceived. Good Luck!!
Each test is different.
I recommend taking First Response when your period is due for the most accurate result. Or up to 3 days before your period if you just can't wait.
some say up to five days but I would definitely wait until you miss your af you test. Good luck!