For healthy growth and good color, cool season lawns need a minimum of two feedings a year, in spring and fall. Luckily, in the NC Piedmont the target dates* for fertilizing your lawn in spring and fall land on holidays that you should be remembering already (if you know what's good for you): Valentine's Day and Thanksgiving. Isn't that convenient?
You should apply 1 pound of nitrogen per 1000 sq. feet for both spring and fall applications. You can figure out how much fertilizer you'll need by dividing 100 by the first number of the N-P-K analysis on the bag. The result is how many pounds of fertilizer to use per 1000 sq. feet. Let's use an analysis of 15-0-18 as an example:
100 / 15 = 6.66 You'll need 6.66 lbs of this fertilizer for every 1000 sq feet (that's 20 feet x 50 feet)
If you have "leftovers" from your lawn's Thanksgiving meal, it can be saved to use for the next season's application if you keep the bag tightly closed in a cool, dry location.
*Of course you don't have to go out and fertilize on Thanksgiving day itself, but it might be a good excuse if the family starts driving you crazy. (Don't even try this on Valentine's Day.)