You shouldn't need a calculator or application. Just remember that the lower the number that you see on the top LCD or in the viewfinder, the more likely your photo will be blurred.
You may want to go into Shutter Priority mode (Marked by an "S" on the mode dial) and set your shutter speed to something around 1/250 or faster. As you zoom in, your aperture will change and the camera will be more prone to bur from your hands shaking, but as long as you're in a well-lit area with an ISO of 400 or above, you have VR on and you're holding the camera pretty steady, you should be just fine.
Enjoy the camera