Adding additional columns in Excel without affecting existing equations

I have completed a very complex Excel spreadsheet with a lot of equations, except ...

I forgot to include September

I have Jan through Dec, all the months, except the calculations for September. Of course all

the equations are currently perfect for the data that's here.

How do I add a whole new column without ruining the previous equations?

PS: tomorrow is my holidays and I have to go to work to finish this table, so bad.

would really appreciate some kind expertise :)

Assuming the following:

The equations are using the format (A1:D1) and not (A1,B1,C1,D1). You want the new data to be FACTORED INTO the equation.

The following will work: Right-click on the column letter above the October column. Click Insert. Type all your data in. Your equation column should reflect your new data.

Please tell me if my above assumptions were incorrect.