Just wondering if I could automatically change a chart.

For example I do a number of chart for every month, obviously days of the
months changes so on a month where there are 31st, there isnt a problem. The
problem is when i have a month which only has 30 or 28 days. This leaves the
last 3, 2 columns zero but are still on the chart but are shown as zero.

Does anyone know how to automatically adjust the source data? perhaps with
an if statement?

Thanks