FORECAST.ETS.CONFINT Function in Microsoft Excel: Syntax, Examples & Troubleshooting

=FORECAST.ETS.CONFINT(target_date, values, timeline, [confidence_level], [seasonality], [data_completion], [aggregation])

The required target is a date/time or numeric index; values and timeline are equally sized historical ranges. The timeline must have a consistent interval and nonzero numeric timestamps. Sorting is implicit. A target earlier than the end of history produces #NUM!.

The optional confidence level defaults to 0.95 and must be strictly between 0 and 1. Supply 95% or 0.95, not 95. Both endpoints 0 and 1 are invalid. Microsoft’s interpretation depends on the forecast model and normal-distribution assumption; it is not a guarantee that a particular future observation will fall inside the bounds.

For seasonality, 1 or omitted means automatic detection, 0 disables seasonality, and another positive whole number sets the pattern length in observations. The maximum is 8760; unsupported values produce #NUM!. A value of 1 is the automatic-setting flag, not a request for a fixed one-observation cycle. Turning seasonality off does not make this function an ordinary least-squares regression formula.

The optional data_completion setting distinguishes missing observations from real zeros: 1 or omitted fills missing points using the neighboring average; 0 treats missing points as zero. Microsoft documents support for up to 30% missing data. A recorded zero already present in your dataset is a value, not an absent timestamp.

aggregation selects how equal timestamps are combined. The individual worksheet reference describes 0 as the default average. Microsoft’s forecast aggregation enumeration, checked October 17, 2026, lists 1 Average, 2 Count, 3 CountA, 4 Max, 5 Median, 6 Min, 7 Sum. These sources do not express the default consistently. The same worksheet page also mentions duplicate-timestamp #VALUE! errors while describing aggregation of duplicates. These documentation inconsistencies were not resolved by native testing. For predictable preparation, aggregate raw records yourself into one value per timestamp. The source workbook used here has unique timestamps, so its examples do not depend on choosing among duplicate-handling methods.

Download Microsoft’s original forecast sample workbook, linked from the official function reference and checked October 17, 2026. On Forecast.ets sample, use all 57 historical rows, with dates in A4:A60 and airport-passenger counts in B4:B60. The history runs from January 2009 through September 2013. A4 is January 1, 2009 (date serial 39814), B4 is 2644539; A60 is September 1, 2013 (41518), B60 is 3781168.

Keep the entire dataset. These endpoint values are an identity check, not enough data to reproduce the fit by themselves. The workbook contains actual stored formulas and cached outputs. Results below are Microsoft-workbook cached results, read without recalculation, not fresh tests in Excel or independently reconstructed ETS estimates.

On Forecast.ets sample, A61 is October 1, 2013. C61 contains the point forecast, cached as 3858196.3569040108. The radius formula corresponding to the saved lower and upper bounds is:

=FORECAST.ETS.CONFINT(A61,$B$4:$B$60,$A$4:$A$60,0.95,1,1)

The workbook stores the bounds rather than a separate radius cell:

Subtracting the cached lower bound from the cached point estimate independently gives a radius of approximately 162369.285566415. The same radius, within floating-point rounding, follows from upper bound minus point estimate. This arithmetic checks the published sample; it does not reproduce Microsoft’s internal interval algorithm.

For A62, November 1, 2013, the cached point forecast is 3562679.8147925721, the lower bound 3395234.3290626127, and the upper bound 3730125.3005225314. The corresponding radius is approximately 167445.485729959.

Use the same formula with A62 as the target, keeping the historical ranges fixed. Notice that this sample’s later horizon has a larger radius even though its point estimate is lower. An interval’s absolute width and the forecast’s level answer different questions.

A reporting sheet can use one point-forecast column, one radius column and two bound columns. With point forecast in C61 and radius in F61, =C61-F61 is the lower bound and =C61+F61 is the upper bound. Round only for display after these calculations.

Use the same history, seasonality, completion and aggregation settings for the point forecast and its radius. Combining an automatically seasonal point forecast with a nonseasonal interval is not a consistent model report. Confidence-level changes affect the interval; do not reuse the 95% cached values as a claimed 90% result.

#NUM! can indicate invalid confidence level, target before history ends, unsupported seasonality or failure to identify a regular interval. #N/A indicates unequal timeline and observation sizes. Clean duplicate timestamps first because the source’s duplicate behavior is inconsistent.

A narrow model interval does not account for every possible future disruption or data-quality error. Check whether past data remains relevant. These sample bounds are historical workbook outputs, not a guarantee of identical current-build values or a forecast for today’s airport traffic.

Microsoft’s reference checked on October 17, 2026 lists: Excel for Microsoft 365 Excel for Microsoft 365 for Mac Excel 2024 Excel 2024 for Mac Excel 2021 Excel 2021 for Mac Excel 2019 Excel 2016. Microsoft’s alphabetical catalog, checked October 17, 2026, identifies Excel 2016 as the introduction-version marker for FORECAST.ETS.CONFINT. This perpetual-release marker does not establish an earlier Microsoft 365 preview or rollout date. Platform restrictions remain separate. The last functioning version is unverified; no retirement is asserted.

The individual reference explicitly excludes Excel for the web, iOS and Android. Use a supported desktop build. The sample workbook’s saved outputs do not establish which current build will reproduce every last decimal. Example verification: ETS fitted results are explicitly Microsoft-workbook cached results, not independently fitted predictions. Only identified arithmetic, reference substitution and display checks are independently derived. These examples have not been tested in Microsoft Excel. No screenshot or native execution is claimed.

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• Microsoft FORECAST.ETS.CONFINT reference, retrieved October 17, 2026.