I have a df where I am calculating values by month. When I run this code on my df it generates the desired results:

for i in range(12,len(df.index)):
    df.iloc[i, 1] = df.iloc[i-12,1]*(((df.iloc[i,3]/100)+(df.iloc[i,6]/100))+1)

So far so good. I want to apply this same formula to more than 1 df so I try using a list & modify the code above. To begin I place my initial df into the list and run the code:

my_dfs=[df]
 
for i in range(12,len(my_dfs.index)):
    my_dfs.iloc[i, 1] = my_dfs.iloc[i-12,1]*(((my_dfs.iloc[i,3]/100)+(my_dfs.iloc[i,6]/100))+1)

But I get the error message:

object of type 'builtin_function_or_method' has no len()

How do I fix this?