First, you don't need SUM() at all in this case. A simple
=D3+D11+D19....
will do. SUM() is usually used for quickly adding contiguous ranges, like
=SUM(D1:D9) [would add all values in D1, D2, D3, D4, D5, D6, D7, D8 and D9

By removing the SUM() function from your statement, you get away from the
limit on number of cells referenced in it, and you move on to a much larger
limit for the total size of contents of a formula.

"acking62" wrote:

I'm trying to total
=SUM(D3,D11,D19,D27,D35,D43,D51,D59,D67,D75,D83,D9 1,D99,D107,D115,D123,D131,D139,D147,D155,D163,D171 ,D179,D187,D195,D203,D211,D219,D227,D235)
I need to extend this further but can't add any more do to error. How can I
add more cells to calculate?