Model a loan balance that rises despite regular payments

If a scheduled payment is smaller than the interest accruing for the period, the unpaid amount must be accounted for under the agreement. Where the terms add that unpaid interest to the loan balance, the amount owed can rise even though the borrower keeps making payments. The cash plan needs to show both the current payment and the growing future obligation.

The Consumer Financial Protection Bureau describes this mechanism as negative amortization in its consumer-loan explanation. The numerical model here illustrates the same balance arithmetic for an explicitly assumed agreement. It does not assume that a particular business facility permits interest capitalization or adopts consumer-loan protections.

Read the actual terms before building the schedule: interest basis, payment date, capitalization rules, minimum payment, balance cap and any later reset. A missed required payment should not be modeled as an agreed financing feature merely because the spreadsheet can add it to principal.

Assume a hypothetical opening balance of $100,000, a 1% rate per monthly period and an $800 payment at each month end. The agreement is assumed to capitalize any unpaid interest monthly. There are no fees, additional draws or rate changes in this example.

In month one, interest is $1,000. The $800 payment leaves $200 unpaid, so the balance becomes $100,200. In month two, interest is 1% of that higher balance, or $1,002. Another $800 payment leaves $202 to be added, producing a $100,402 balance.

The second month's interest is larger because the previous unpaid amount is now part of the balance under the assumed terms. A schedule that calculates every month's interest on the original $100,000 would miss that effect. A schedule that subtracts the entire $800 as principal would move in the wrong direction entirely.

Repeating those assumptions for 12 periods gives an ending balance of approximately $102,536.50. Cash payments total $9,600. Total interest accrued is approximately $12,136.50, reconciling through $100,000 opening balance plus interest less payments to the ending amount.

The $2,536.50 increase is larger than twelve times the first month's $200 unpaid interest. The extra $136.50 arises from interest on the amounts capitalized during the year. That difference is small in this example but becomes more consequential with a longer period, larger shortfall or different rate.

Keep enough calculation precision to reproduce the lender's stated rounding convention. Rounding every internal balance to whole dollars can accumulate differences over a long schedule. Present rounded amounts to readers while retaining the underlying calculation and any contractual per-period rounding rule.

Suppose the hypothetical terms then require the $102,536.50 balance to amortize over 24 equal monthly payments at the same 1% periodic rate. The standard level-payment formula is balance multiplied by the rate, divided by one minus (one plus the rate) raised to negative 24. It produces a payment of approximately $4,826.75.

That later cash requirement is much larger than $800 because it now covers interest and repays the accumulated balance over a defined remaining term. It is a consequence of the assumed schedule, not a prediction of what a lender will offer or permit.

Put the reset payment in the forecast before assessing the affordability of the initial payment period. A near-term cash improvement can coexist with a later funding problem. Show the first reset date and the period when cash is tightest rather than reporting only an average monthly payment across the full loan life.

Identify fees added to the balance separately from unpaid interest. A capitalized fee can make the debt grow even when the payment covers all periodic interest. Keeping those movements separate prevents the reviewer from attributing the entire increase to negative amortization and makes the next period's interest base easier to reconcile.

A balance cap may trigger an earlier reset or another contractual consequence. Compare the projected balance with that cap at each relevant date. Do not assume the low-payment period lasts to the nominal end date if another term can end it sooner.

A floating rate can change the amount of unpaid interest even if the cash payment initially stays fixed. Model the stated rate mechanism and plausible rate paths separately from the payment rule. A fixed payment is not evidence of a fixed borrowing cost.

Some payments may change with an index, percentage or scheduled step rather than stay at $800. Implement the actual rule with its dates and limits. An assumption carried forward from the first statement can understate later required payments or overstate the balance if the borrower has begun paying more.

The agreement determines whether an unpaid amount becomes principal, remains accrued interest or creates a payment default. Accounting may also distinguish contractual principal, carrying amount, accrued interest and fees. Ask the accounting owner to reconcile those categories rather than force every difference into one loan-balance cell.

A cash payment and an interest expense are separate events in the schedule. The company may incur more interest than it pays during the period. Keep the accrual and payment dates visible so management does not read the smaller bank outflow as the full financing cost.

Reconcile to each lender statement and investigate changed rates, fees, payment applications or capitalization dates. A growing balance can follow the modeled terms, but it can also reveal a missed payment or an input error. The explanation should come from the agreement and transaction record, not from the model's ability to produce a similar total.

If management considers additional payments or different financing, start with the current supported payoff amount, future payment schedule and any applicable charges. Preserve the original loan history for accountability while comparing the cash flows that can still change.

The useful output is a dated schedule showing payments, interest, capitalization, principal movements and the later repayment requirement. It makes the tradeoff visible: less cash paid now can leave a larger balance and a different future cash commitment under the agreed terms.