An NYPD cop fatally shot himself inside his home on Staten Island on Monday, police sources told The Post.

The officer, whose identity was not immediately released, was supposed to go to the firing range Monday morning for qualification reasons, and when he didn’t show up, police sent someone to check on him as part of protocol, sources said.

The cop, who worked in the 121st Precinct, was found dead inside his Great Kills home on Tanglewood Drive near Arthur Kill Road around 10:50 a.m., according to sources.