Soo my so called menses would have been expected on the day I take my beta pregnancy test 5/3/2018…

Soo my so called menses would have been expected on the day I take my beta pregnancy test 5/3/2018 (4days from now) I’m 3dp5dpt so would that be like 8dpo right? Would it be safe to test 4 days before my expected “menses”? + or -?