future trading day calculation

["john a hamon (on the mark)" <jhamon@xxxxxxxxxxxxxxxxx>]

has anyone got any suggestions on how to calculate future trading dates?
for example, if i want to determine the calendar date of 20 trading days
from today.  

i would prefer to do the work in excel, but if there is an easy language
approach, i'd be interested in that too.  

thanks for your help,

jh
john hamon
on the mark, llc

760/634-4850