Double Exponential Smoothing

Formula

$$\begin{array}{rl}{S}_t& =\alpha X_t+(1-\alpha )(S_{t-1}+T_{t-1})\\ T_t& =\gamma (S_t-S_{t-1})+(1-\gamma )T_{t-1}\\ F_{t+h}& =S_t+h{T}_t\end{array}$$

Tip

Involves two smoothing parameters ($\alpha$ and $\gamma$) for level and trend.