How early can you tell, with just a pregnancy test alone, whether your pregnant or not?

Joetta
I am late by several days, but on top of this I also have an irregular cycle. Also, we already know that it may be impossible for us to even conceive. I know I am capable of having kids. I already have a seven year old and five year old. But he honestly doesn't know if he is capable. But if there was a slight chance I was wondering how early can I get a good reading just from a home pregnancy test alone? Thank you in advance for your answers. :)