Start with a permanent record of the original loan terms
Keep the original principal, interest rate, first payment date, payment frequency, scheduled payment, amortization term, and maturity date in one place. Do not overwrite the original terms every time something unusual happens. The scheduled loan is your baseline; the transaction history is the record of what actually occurred.
Record every actual payment as a transaction
For each payment, record the date received and the amount received. Then preserve how the payment was applied to interest, principal, fees, escrow, or another category. This matters because two payments of the same dollar amount can affect the balance differently if they are received on different dates or applied differently under the note.
Keep scheduled installments and actual transactions separate
The installment schedule answers what was supposed to happen. The transaction ledger answers what did happen. Keeping both views avoids a common bookkeeping problem: changing the schedule until it looks like the payment history and then losing the original obligation.
Handle partial, extra-principal, and late payments explicitly
A partial payment should remain visibly partial instead of being treated as if the scheduled installment was fully paid. Extra principal should be identified separately so it can reduce the balance correctly. Late-payment treatment, fees, and interest accrual should follow the loan agreement and applicable rules rather than a generic assumption.
Reconcile the current balance regularly
After posting payments, compare the calculated principal balance with your prior statement or internal record. Regular reconciliation makes errors easier to find while the supporting information is still available.
Prepare year-end totals from the same ledger
The same payment records can be summarized by calendar year to show principal received and interest received. Those figures are useful for accounting and review, but tax reporting requirements should be confirmed with the appropriate tax professional.
Track the actual loan after it is made
Private Loan Manager for Windows keeps the loan terms, transaction history, balances, delinquency status, payoff information, and year-end principal and interest totals in one local desktop program.