Obtaining forecasts

A multiplicative model is equivalent to an additive model for the log data.

log(Data)   =   Seasonal*   +   Trend*   +   Cyclical*   +   Residual*

This model will give forecasts of the log data.

forecast of log(Data)   =   (forecast Seasonal*)  +  (forecast Trend*)  +  (forecast Cyclical*)

To obtain forecasts in the original scale, an inverse transformation must be applied. With base-10 logarithms,

forecast of Data   =   10 forecast of log(Data)
 

(If natural logarithms were used, an exponential function gives a forecast in the original units. Both types of logarithms result in identical forecasts.)