Calculating a final payment when rounding down monthly charges

Question

Here is the situation:

Monthly charges are applied to an account, and are rounded down to the nearest dollar. This creates a final payment that is higher than the other payments if there is any remainder on the monthly charges. If all of my debtor's had accounts like this, there would be no problem determining a final month, as the number of months are set, and I can check that against the number of charges on their account and just charge them the balance on their accounts on the final month.

However, it gets more complex. Now, the total due can change at any given time during repayment because it might be found out that the debtor owes more or less. Again, this would be no problem to calculate the final payment, but the people setting the payments base the new payment amounts off of the total originally due, say $1000, as opposed to the current balance on their account, say $800. When this happens, accounts can be paid off either ahead of their stated number of months, or beyond their number of months. The second of which is not allowed, and I have to determine when that final payment should occur and charge the balance. This might not be too difficult, but you not only have to track the differences in the payment amounts from before and after the total due change, but you also have to track the remainder from the payments being rounded down.

This goes even one step further and debtors are given an ability to lower their payments. This new payment amount is also based off the total due instead of the current balance, once again leading to payments closing an account either before or after it is supposed to.

Is there anyway, that you can calculate when these accounts are on their final month, and apply the balance remaining to their account charge?

The majority of accounts are straight forward and do not have payment amount changes, but many still do.

Answer 1

Seems to me you want to maintain a [total debt], [total paid], [Monthly payment] column for each borrower. Then when [Monthly payment] > [total debt] - [total paid] they are in their last month?

Hope this helps