I tested exactly on the day of my missed period because I wanted to confirm before continuing my workout routine. Once it was positive, I immediately consulted my doctor to see if my daily brisk walks were safe to continue.
I totally understand that burning curiosity and the sweet anxiety of wanting to know immediately. Try to wait patiently until the first day of your missed period to avoid getting a heartbreaking false negative.
I tested on the day of my missed period and got a very faint line. It is best to wait until at least 1-2 days after your missed period so your body has enough HCG for a clear result.
With twins, my HCG levels were super high so I got a dark positive even 2 days before my missed period! But practically, save your money on multiple kits and just test 2 days after your due date.