How Many People Have Been Killed by Guns Since Newtown?

This is from the Slate website by Chris Kirk and Dan Kois: 

Using the most recent CDC estimates for yearly deaths by guns in the United States, it is likely that as of today, 7/30/2013, roughly 19,684 people have died from guns in the United States since the Newtown shootings. Compare that number to the number of deaths reported in the news [6,666, see site] and you can see how undertold the story of gun violence in America actually is.