The question is, what formula?
If you are refering to =SUM(D4:R4), originally in T4, then I don't see the logic in this remaining unchanged if columns are added, as Column T is "Total No" surely this should total the row? ... 
My logic says that this should actually be =SUM(D4:S4).
Not affecting the column 'U'
Column U doesn't have a formula, do you think sugavanam means Column T should remain unchanged?
Check the formula I have in "Total No" after you run the code.
P.S. the only other formulae I can see are =I552*#REF! and =J552*T560 in columns I & J, they look like mistakes to me.
For your benefit look at these rows of code as a way to avoid loops
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