Macro/formula ideas for chart that pulls up only last 12 months of info?

[itregub]

I'm working on a bar graph chart that accumulates data from the last 12 months of information (each month is a distinct data point). Every month, I'm supposed to extend the sum to the most recent data point and subtract the oldest data point from the total (since "12 months ago" now would become "13 months ago" and outside the scope). Is there a formula or macro I could use to automatically tell Excel to always some up the 12 most recent data points? Thanks!

[Chance2]

You can use named ranges with the OFFSET function to limit you to the last 12 data points.

For example, you can define a name as xVal

=OFFSET('Sheet1!$B$3,0,COUNTA('Sheet1!$B$3:$IV$3)-12,1,12)

And then use Sheet1!xVal as the x-axis of the chart.

You would need a different named range for each series and each label (if it is moving).

The example OFFSET is for adding a new column of data.