how to stop auto adjusting formulas when insert reference column

[mystockpick]

A1 reads =+(B1+C1)/C1 where B1 represents 'the current month' and C1 represents 'the previous month'. The formula in A1 shows me the change between the current and previous months. Each month I want to insert a new column between A and B, and, I want the formula in A1 to remain as =+(B1+C1)/C1.

I've tried different things, but it seems no matter what I do, when I insert a column between A and B, the formula in A1 changes to =+(C1+D1)/DC1

Any thoughts?
Thank you.

Joe