Here is my Office 365 LAMBDA Excel Formula that can be used to perform Exponential Smoothing on a range of values including the use of an Alpha value alongside the initial priming value. You can use this type of Function to create a 'smoothed' level as an input into a Forecast Model Back · Purchase

=LAMBDA(ARRAY,ALPHA,INITIAL_VALUE,
        SCAN(INITIAL_VALUE,ARRAY,
        LAMBDA(PRIOR_VALUE,CURRENT_VALUE,ALPHA*CURRENT_VALUE+(1-ALPHA)*PRIOR_VALUE)))($D$28:$R$28,0.4,$D$28)

Add a Named Range called ExponentialSmoothing and then Copy & Paste the formula below:

=LAMBDA(ARRAY,ALPHA,INITIAL_VALUE,
        SCAN(INITIAL_VALUE,ARRAY,
        LAMBDA(PRIOR_VALUE,CURRENT_VALUE,ALPHA*CURRENT_VALUE+(1-ALPHA)*PRIOR_VALUE)))

Use the Function like this in any Worksheet in Excel for a range of any size ($D$28:$R$28 are the actuals, 0.4 is the Alpha coefficient and $D$28 is the initial priming cell / first value):

=ExponentialSmoothing($D$28:$R$28,0.4,$D$28)

Chart demonstrating the LAMBDA Exponential Smoothing Function on a range of 15 values with an Alpha coefficient of 0.4