How to calculate GDP growth rates

I see a lot of hits from people doing Google searches on the phrase “how to calculate GDP growth”—so I decided to make it more explicit and easier to find.  If you aren’t interested in the math, skip this post.  If you are, click on the two thumbnails; the first one (at left) is the math, the second one (at right) is an example using real GDP (USA) from Q4 2005 and Q2 2006.