>I suppose its standard.
I still don't have a clear idea what you want to calculate; I suggest you take a look at the different financial functions offered by Excel, and see which one resembles what you want to calculate.
Since Excel has different function names in different languages, to discuss the implementation of a specific function here, you can save a macro to see the function name in English.
Difference in opinions hath cost many millions of lives: for instance, whether flesh be bread, or bread be flesh; whether whistling be a vice or a virtue; whether it be better to kiss a post, or throw it into the fire... (from Gulliver's Travels)
