What is Forecasting in Tableau?

Forecasting projects a measure forward in time using exponential smoothing, fitted automatically from the historical values in the view.

It requires a date dimension and at least one measure, and enough history to work with — Tableau wants several periods, and more for a seasonal pattern to be detected. Turn it on from the Analytics pane by dragging Forecast onto the view.

The model considers level, trend and season, choosing among the candidates by fit. Forecast Options lets you set the horizon, force or exclude seasonality, and show prediction intervals.

The important caveat, and the one interviewers like: it extrapolates from the past and knows nothing about the business. It cannot anticipate a price change, a competitor, or an event outside the data — so it is a baseline expectation, not a plan.