There are a few different formulas to calculate IBU's Rager formula, tinseth, hopville, etc. Each different formula gives you a different reading. I typically use tinseth when i calculate my recipes.
Also take a look at the water volume they suggest in the recipe as more or less water will also change the Ibus of a recipe.
primary:15 minute Cascade Pale Ale
Primary 2: Cream of 3 crops
Primary 3: Sam Adams Holiday Porter Clone
bottled:BM's Blue Balls Belgian Wit
15 Minute Cascade Pale Ale
DryHopped Cream of 3 Crops