# Re: Rolling Calculations

*From*: Harlan Grove <hrlngrv@xxxxxxx>*Date*: Wed, 05 Sep 2007 17:13:29 -0700

Motaad <Mot...@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote...

I have a spread sheet with three years of monthly data. I need to....

calculate for a rolling twelve month total each month.

(i.e.)

sum data in columns for (Jan2006 - Dec2006),

sum data in columns for (Feb2006. - Jan2007),

sum data in columns for (Mar2006. - Feb2007, etc.)

How are the months identified? Is the data grouped by year in fixed

size chunks, e.g., each month's data spans 20 rows? Is there another

column with dates?

If column A contained dates and column B the data you want to sum,

both spanned rows 1 to 10000, and if Jan2006 thru Dec2006 were the

first 12 month period to sum, then try the following.

D1:

=SUMIF(A$1:A$10000,">="&DATE(2006,ROWS(D$1:D1),1),B$1:B$10000)

-SUMIF(A$1:A$10000,">="&DATE(2007,ROWS(D$1:D1),1),B$1:B$10000)

Fill D1 down into D2:D36. Another alternative, shorter, more efficient

but also more complex, would be

D1:

=SUMPRODUCT(--(ABS(12*(2006-YEAR(A$1:A$10000))+5.5

-MONTH(A$1:A$10000)+ROWS(D$1:D1))<6),B$1:B$10000)

which you'd also fill down into D2:D36.

.

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