In the case of a 30/360 interest base loan where the payment is due on the 1st of each month, is the payment not 30 days past due when the month has 31 days and the payment hasn't been made by that day?

Thanks for any input.

30/360 is used for interest calculations, not to determine past due status.

For mortgage loans (more than other types) it says that basically 1/12th of the annual interest is due each month, rather than calculating the interest due based on time between payments (simple interest).

From the call report instructions:

(1) Closed-end installment loans, amortizing loans secured by real estate, and any other loans and lease financing receivables with payments scheduled monthly are to be reported as past due when the borrower is in arrears two or more monthly payments. (At a bank's option, loans and leases with payments scheduled monthly may be reported as past due when one scheduled payment is due and unpaid for 30 days or more.)

I would not take the option.