The safe answer: Wait until your period is due or late. This will give you a fairly accurate answer.
*But what's the fun in that?*
Many of us ladies have an addiction. It's not pretty, and it can get really expensive. But, we can't help it.
IF you are charting or using opk's it is much easier to say when you can start testing. Personally, I've started early a couple times, but genuinely the goal is to wait until 9-10 dpo (days past ovulation) Mind you will probably get a false negative that early, however, you *could* catch a glimps of a possible (sometimes definite) positive. That you can then worry about over the next 3 days as you take more tests then you've had birthdays (It's a vicious cycle). But, this is not for the faint of heart, if the thought of a negative makes you want to cry, please wait until you are at the end or past your normal lp to test.
Good luck! Feel free to come here with all the 'is this a line?' questions you may have!
~Baby dust~