Grace days for late charges

Hi,

I have a business case and  I hope  you can  help  me  to resolve it.

We already  activate  all functionality  for late charges  but  in  Customer   Profile Classes  we  set  Receipt Grace Days as 30.

Customer Number:  3001-7

Payment Term: 45

Receipt Grace Days: 30

Invoice amount: 150,000.00

Days late: 31

Expected result: calculate interest only  for  1 day after  Receipt Grace Days.

Actual Result: calculate interest  for 31 days

Thanks in advance.

Jaquelin