FORECAST.ETS.SEASONALITY function

Tells you the season length Excel found in your data (for example 12 for a yearly pattern in monthly data).

Works in desktop Excel only

Syntax

=FORECAST.ETS.SEASONALITY(values, timeline, [data_completion], [aggregation])

How to use FORECAST.ETS.SEASONALITY in Excel, step by step

FORECAST.ETS.SEASONALITY doesn’t run in a web practice sheet because it uses Excel’s own exponential smoothing engine (AAA version of ETS). Follow these steps in Excel itself.

You’ll need

Excel 2016 or later
An evenly spaced timeline

Lay out the history. Dates in A2:A37, values in B2:B37.
Ask for the season. Type =FORECAST.ETS.SEASONALITY($B$2:$B$37,$A$2:$A$37).
Read the answer. 12 means a pattern that repeats every 12 points; 0 means no seasonality was found.

Example

=FORECAST.ETS.SEASONALITY($B$2:$B$37,$A$2:$A$37)

Result: 12

Use the result as the seasonality argument of FORECAST.ETS to keep forecasts consistent.