Glad that info helped!

As for the average - that's a great feature to add to a graph. If you've created the data range for Jan through Dec, just add one more line called "Average" and in that cell, put =average(a1..a12) which would cover your Jan-Dec data range. Also, make your graph data series include this average line. Now, when your formulas update for March, the average updates as well.

But there's a catch: the =average formula will include the zero's which are in the cells that have not been completed yet, thereby skewing the average. However, =Average() will exclude blanks. So you'll need to modify each formula to include an if statement like this: =IF(C4="","",+D4). This IF statement looks at one of your data entry cells (C4). If its blank (i.e. you haven't put data in for that month yet), then it makes this cell blank and it will be ignored for the average. If C4 isn't blank (you HAVE entered data), then retrieve the relevant data (+D4) for this cell. The math occurs, it provides a value which shows on the graph, and the average calculation is relevant. Follow?

Again, going back to an earlier idea, you could just insert a new line each month and copy the formulas down to the new line and the graph would insert the new column and update the average. I've done it both ways. Purely depends on how much you'll use the worksheet going forward, and how user-friendly you want it to be for each future use.

Once you've figured out this general framework, you will end up re-using this concept with future graphs. Your questions are good ones for making the graphing mindlessly easy for the users going forward. Its a great return on investment.

As for predicting the remainder of the graph, I've never tried that but I think its possible in Excel. Maybe someone else can jump in with that expertise?

Matt