This document discusses forecasting with seasonality. Seasonality refers to periodic fluctuations that repeat over time, such as yearly or quarterly patterns. It is important to account for seasonality when developing forecasts. There are two main ways to incorporate seasonality into forecasts. The first method is a three step process that involves calculating a seasonal index and adjusting the forecast accordingly. The second method is a four step process that also uses a seasonal index to adjust the raw forecast to account for typical seasonal variations. Examples are provided to demonstrate how to calculate seasonal indices and generate seasonal forecasts.