Based on the size of your data set, the easiest thing to do is calculate the forecast in Excel, add a "Forecast Column" (e.g., forecast/actual), then in Tableau drop the forecast column into the color shelf. See workbook for example.
There is probably a very complex way to do this in Tableau with some type of really well thought out parameter and table calculation solution; but if it takes you 8 hours to figure out and code vs 2 min a month to do in Excel, your ROI has a long tail.
Good KB article here
I try to avoid forecasting in Tableau if I can help it. Now in Tableau 8 they are introducing a forecasting module which will create a few simple forecasts, which I'm excited for!
Forecasting Example.twbx.zip 16.5 KB
But I really need to do it in Tableau because this is not only for reporting and visualization, but also for “What If” scenarios that are built into a economic forecasting model with several variables and inputs which work very good in Tableau, but I cannot figure out how to calculate the future values and the plotting.
Thanks for sharing your example. There are some new features in the Tableau 8 Beta that can potentially help. However, I strongly advise adding another two years of historical data. This would be of great help in either formulating an "expert" (i.e.-human estimated forecast) and in actually computing an accurate statistical model forecast. My biggest fear is the seasonality of your data is unknown without two complete years of data and in many business scenarios, this is often critical to good forecasts.
If you could repost this and send me a quick e-mail at (split up to stop robots from reading it)
that would be great.
Director of Analytic Product Management