Safe Sex

Hi po. Totoo po ba na 7days before and after ng menstruation ay safe to have sex? Kase po last mens ko Dec 2-5, then ang edd ko is Sept 7. Pano po ba nalalaman yung bilang nyan? I want to know po kung anong exact date kami nakabuo ni hubby. Kase calendar po ginagamit namin so hindi po yung accurate?