Which Is The Safest Day Of The Menstrual Cycle To Avoid Pregnancy?

Hi
i am married, i just want to postpone pregnancy for few month, but i enjoy unprotected sex and wanted to have it, could pls. inform me on what probable days, this unprotected/direct sex can prevent pregnancy starting from day 1 of MC
, i have heard of this, there are specific days on which pregnancy can occur

also inform if wanted have pregnancy, which are days starting from day1 of MC , this pregnancy can occur