FORECAST.ETS.SEASONALITY Function in Excel: Which Cycle Did Excel Find?

FORECAST.ETS.SEASONALITY Function in Excel: Which Cycle Did Excel Find? featured illustration

📎 This article includes 1 downloadable practice file ↓

⏱ 2 min readUpdated 5 October 2026

StatisticsLevel: ExpertAvailable in: Excel 2016+

In this article
  1. Syntax
  2. Examples
  3. Example 1
  4. FORECAST.ETS.SEASONALITY in practice
  5. Where you will use it
  6. Worked example
  7. Mistakes people make
  8. Related functions
  9. Continue learning

FORECAST.ETS.SEASONALITY reports the season length Excel detected — 12 for a yearly cycle in monthly data, 7 for a weekly cycle in daily data.

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Syntax

=FORECAST.ETS.SEASONALITY(values, timeline, [data_completion], [aggregation])
Argument What it means
timeline Evenly spaced dates.

Examples

Example 1

=FORECAST.ETS.SEASONALITY(B2:B37, A2:A37)

Should return 12 for three years of monthly sales with a festive peak.

FORECAST.ETS.SEASONALITY in practice

Where you will use it

  • Detect the season length Excel uses
  • Check weekly vs monthly patterns
  • Validate forecast settings

Worked example

SeriesFormulaResult
Weekly pattern (7)=FORECAST.ETS.SEASONALITY(INDEX($I$1:$K$28,0,ROW()-1),$H$1:$H$28)7
Quarterly (4)=FORECAST.ETS.SEASONALITY(INDEX($I$1:$K$28,0,ROW()-1),$H$1:$H$28)2
No pattern=FORECAST.ETS.SEASONALITY(INDEX($I$1:$K$28,0,ROW()-1),$H$1:$H$28)0

Results calculated in Excel.

Mistakes people make

MistakeWhat to do instead
0 resultNo seasonality detected
Short dataNeeds several cycles

FORECAST.ETS

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📎 Practice files for this article

  • 📗
    Practice workbook: Statistics advanced33 tasks on realistic sales data — type your formula, the Check column turns green when it is right. Answers sheet included.
    ⬇ XLSX · 36 KB

Free to use for learning. Files with macros (.bas) are plain text — import them with Alt+F11 → File → Import File, and always test on a copy.

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