For this exercise, I’ve taken numbers from one website I used to manage as an example. You’ll see I’ve filled in on the horizontal months. They actually start at December 2005, but for the sake of clarity I’ve only shown here 2009 through to the end of 2014. In other words I’ve taken the last three years’ worth of data for forecast the next 2. Ideally, you should try to go as far back as you possibly can, even if it’s only one month here and there – it’ll give you more background on which to rely.