I am trying to create a forecast using a monthly timeseries data set of marketing expenses for a fictional company. The data looks something like this:
Using linear regression to forecast future sales, I get the following result:
My problem lies with the seasonality of the marketing expenses (higher in the summer months for instance). I would ideally like to calculate to forecasted values of future months including seasonality. I read somewhere about ARIMA forecasting, but am really searching for some best ideas on how to accomplish the task.
To be clear, I do not JUST want a chart and trendline, but the data to support it too.
Any help would be much appreciated!