I would like to forecast likely future demand based on historical demand. The problem is: I have no mathematical background and in relevant tutorials and even in literature formulas are used, that depend at every step on a given value for that time period, or in other words you need to know the value that you are forecasting, which seems either pointless or the word "forecasting" is used different in this context than in everyday language.
I am sure you know common models like Holt or Holt-Winters. For trended data, formulas are:
Current Forecast = alpha * Current demand + (1-alpha) * (Last Demand + Last trend)
Current trend = beta * (Current Forecast - Last Forecast) + (1-beta) * Last trend
As you can see, current trend depends on current forecast, and current forecast depends on current demand.
What do I do when I want to forecast future values for demand of a product when it has a trend? Please imagine the following list as a table because I dont know how to format the text properly:
Time period: 1, 2, 3, 4, 5, 6
Demand of waffles: 10, 11, 10, 13, 15, 16
I know I just could calculate a trend line in excel, but for several reasons I need to understand forecasting models (in a second step also for seasonal data).