Say that your datalist goes from G3 to G99.

You could enter this in G2 or G100, or wherever:

=SUMPRODUCT((MOD(ROW(INDIRECT("G3:G99")),3)=0)*IND IRECT("G3:G99"))

--
HTH,

RD

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"Vivian" wrote in message
...
I need to sum up a column of noncontiguous cells.
(eg. G3+G6+G9+G12); with the result being presented at
the bottom of the column.

However, whenever I insert rows in between the data and
the row that contains the total sum, I need to manually adjust the
summation
formula.(eg. formula above + G15+G18+G21).
On the other hand, when I delete the rows in between the data and row that
contains the total sum, a reference error pops up. (so I need to manually
adjust my formula again)

I have at least 50 columns to perform this summation for. Is there any
sort
of formula that helps to minimize the manual labour?

Thanks you in advance!