I'm doing my own head in !!

Sorry for the dumb question, u would think I'd no this by now, but I'm now 1dpo and shouldn't be thinking so far ahead (hey I think to much lol) anyway, how many dpo could I start testing? I no implantation won't happen for a few days yet, I'm just curious. I've never actually planned my pregnancies in the past just had the "if it happens then hey" attitude but now ttc our last baby which will also be our rainbow xx