When is a digital test fully accurate?

I want to take the digital test (one that actually says pregnant or not) but in your experience when are they fully accurate? I am 18 dpo (but think that's not right as these tests taken today and yesterday are way too faint)

Any help or advice please. I took the test with the stick yesterday and the strip this morning but as you can see they are extremely faint... My period was due on Monday....

Thanks