Depends on how it's made.
If the flavoring is "infused" before or during the roasting process, then maybe 2 calories a cup... because you'd get that any way with regular coffee (from the natural oils in the beans). Whole infused beans may (or may not) look like they have a little bit of powdery coating on them, depending on what the flavor happens to be, or they may have a shinier surface which doesn't look all that different from regular roasted beans that have natural bean oils. If you're buying a regular coffee, you want shiny beans. The older the beans, the less glossy and shiny they will look.
But if you have an instant coffee that comes as a powder, almost always they will have added sugar along with the flavor. Those flavored "International Coffee" tins are like this, and can be around 40-120 extra calories per cup if they add both sugar and powdered milk.
Edited by: RACKMYBRAINS at: 9/10/2012 (10:58)