VBA Linear Interpolation

Hi All

I have a quarterly US GDP data from 1980 to date. The problem I have is given the data is only produced quarterly I have gaps in the data. This is fine when drawing a chart in excel as you can simply join data points however, an external provider I use to publish charts does not have this feature on its software and I am required to provide a value for every date. I therefore need to interpolate (linear) the values between data points. This is easily done manually on a small data set however I wonder if anyone has a piece of VBA code to speed things up.

Thanks