How soon before your expected period can you take a test?

I have 2 sons, 6 and 10,and am wondering how soon before your next period can you take a test w/o a false result? Also does it have to be a certain test or can you rely on a cheap one? I am due to have my period on Feb.28th and I usually experience some tell tale signs of it , and this month have none of those signs, cramps and so forth.

Im only 14 so I might not be much help, but I was watching this comercial for this pregnancy test, and it said that it could detect wether your prenent or not 5 days before your next period. They made it seem like a big deal so im guessing five days is a lot. Im sorry but I cant rember what brand it was.
hope more expierenced people can help you!

Yes, 5 days before your missed period is generally the earliest. This is when I found out I was pregnant with my daughter and I took the FIRST RESPONSE pregnancy test. The line was faint, but it was there. It gradually became darker as I took more tests just to be sure. Good luck with everything.