if you don't like defining the ranges via the offset method, you might try
renaming all the series as names and creating the charts via a macro

"Mike" wrote:

I have a big Excel doc with numerous charts, each with numerous lines.

About once per month, I need to extend the charts for about a month. This is
a very painful process for each graph (multiplied by numerous graphs!).

Does anyone have any simple method to do a mass change, standard or VBA?
This would be extremely helpful.

I also noticed some posts using OFFSET, but this would be too confusing for
my father (for whom I am doing this) and too cumbersome. Something like a
standard function or a VBA macro that I can program would make his life so
much easier.

Thanks much!