What it means
Every loan payment does two jobs: it covers the interest that has accrued since the last payment, and whatever is left over reduces the principal. Normal amortisation means the second part is positive, so the outstanding balance falls a little each period.
Negative amortization reverses that. When the scheduled payment is smaller than the interest due, the shortfall is capitalised, meaning it is added to the outstanding balance, and the next period's interest is charged on the larger figure.
The effect compounds quietly, which is why balances can drift upwards for years without the borrower really noticing. The structure turns up in several places.
Graduated-payment and option-payment mortgages allow a low starting payment, income-driven student loan plans can accrue more interest than the payment covers, and payment-in-kind corporate debt lets a borrower add interest to principal rather than paying cash. It is not automatically a bad deal.
A business with lumpy cash flows may deliberately defer interest during a construction phase and repay once revenue arrives, and lenders price that flexibility into a higher interest rate. The danger is a borrower who does not understand that the balance is climbing while they keep paying on time.
Most contracts include a cap for exactly that reason. A typical mortgage will state that once the balance reaches, say, 110% or 125% of the original loan, the payment resets to a fully amortising level, which can mean a sudden and painful jump in the monthly cost.
In practice
Real-world examples.
Example
A homeowner chooses the minimum payment option on a flexible mortgage during a year of reduced income. Twelve payments later the balance is higher than when they started, and the lender's annual statement shows deferred interest of just over $6,000 added to the principal.
Example
A graduate on an income-driven repayment plan pays $180 a month against a loan accruing $310 a month in interest. The $130 monthly gap is added to the balance, so the debt grows even though every payment is made on schedule.
Example
A private equity buyer funds part of an acquisition with a payment-in-kind note at 11%. No cash interest is paid for the first two years, the accrued interest is rolled into the principal, and the sponsor plans to refinance the enlarged balance once earnings recover.
Formula
Calculation
New balance = opening balance + interest accrued - payment made, where monthly interest accrued = opening balance x annual rate / 12.
Take a $300,000 mortgage at 6% a year with a first-year payment option of $1,000 a month. Interest for month one is $300,000 x 0.06 / 12 = $1,500, so the $1,000 payment leaves a $500 shortfall and the balance becomes $300,000 + $1,500 - $1,000 = $300,500.
In month two, interest is $300,500 x 0.005 = $1,502.50, the same $1,000 payment leaves a shortfall of $502.50, and the balance climbs to $301,002.50. Carry that pattern through a full year and the balance reaches about $306,168, an increase of roughly $6,168 on a loan the borrower has been paying every single month.Case study
Seen in the real world.
Tidewater Storage Partners is a fictional self-storage developer created purely to illustrate the mechanics. Tidewater borrowed $9,000,000 at 11% to build four sites, and negotiated a two-year payment-in-kind period so that no cash interest would leave the business while the sites were filling up.
The arithmetic was straightforward and unforgiving. After one year the balance was $9,000,000 x 1.11 = $9,990,000, and after the second year it was $9,990,000 x 1.11 = $11,088,900, an increase of $2,088,900 without a single missed payment. When occupancy reached only 71% instead of the 85% in the plan, the refinancing bank valued the four sites at $12,400,000 and would lend just 65% of that, or $8,060,000.
Tidewater had to find $3,028,900 of fresh equity to bridge the gap, at terms far worse than the original investors expected. The illustrative point is that negative amortization moves the risk into the future rather than removing it, and the future arrives with the balance grown.
Watch out
Common mistakes.
- Believing that paying on time means the debt is going down. With negative amortization every payment can be made in full while the balance rises, because the payment never covers the interest.
- Comparing loans on the monthly payment alone. A deferred-interest structure can show the lowest payment on the page and the highest total cost over the life of the loan.
- Forgetting the recast. When the balance hits the contractual cap the payment jumps to a fully amortising level, and that reset is where most borrower distress actually happens.
Questions
People also ask.
Is negative amortization the same as a missed payment?
No, the payment is made and accepted as agreed; the shortfall against interest is simply added to the balance rather than treated as arrears.
Does the capitalised interest earn interest itself?
Yes, once unpaid interest is added to the principal it becomes part of the balance on which future interest is calculated, so the cost compounds.
Is it ever a sensible choice?
It can be, where income or occupancy is genuinely expected to rise, but only if the borrower models the ending balance and confirms the asset value will still cover it.
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