AR Promissory Notes

We are looking to setup Promissory Notes for overdue A/R Accounts. The Setup of the Note and closure of the AR is straightforward, but wondering how others are handling the calculation of interest associated with a Note.

For instance, are you performing the calculation of interest offline in a spreadsheet, using some existing functionality in JDE (e.g. Finance Charges), have created custom JDE application, or are you using a 3rd Party Bolt On (which one?) that interfaces with JDE?

Thanks.