In finance, negative amortization, also known as “Neg Am”, occurs whenever the loan payment for any period is less than the interest charged over that period so that the outstanding balance of the loan increases. As an amortization method the shorted amount (difference between interest and repayment) is then added to the total amount owed to the lender. Such a practice would have to be agreed upon before shorting the payment so as to avoid default on payment.

The term is most often used for mortgage loans; corporate loans which have negative amortization are called PIK loans.

Neg Am is also known as deferred interest or Graduated Payment Mortgage (GPM). This method is generally used in an introductory period before loan payments exceed interest and the loan becomes self-amortizing.

Negative amortization only occurs in loans in which the periodic payment does not cover the amount of interest due for that loan period. The unpaid accrued interest is then capitalized monthly into the outstanding principal balance. The result of this is that the loan balance (or principal) increases by the amount of the unpaid interest on a monthly basis. The purpose of such a feature is most often for advanced cash management and/or more simply payment flexibility, but not to increase overall affordability.

Neg Ams also have what is called a recast period, and the recast principal balance cap is based on Federal and State legislation. The recast period is usually 60 months (5 years). The recast principal balance cap (also known as the "Neg Am limit") is usually up to a 25% increase of the amortized loan balance over the original loan amount. States and lenders can offer products with lesser recast periods and principal balance caps; but cannot issue loans that exceed their state and federal legislated requirements under penalty of law.