Negative amortization

In finance, negative amortization, also known as NegAm, is an amortization method in which the borrower pays back less than the full amount of interest owed to the lender each month. The shorted amount 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. Also known as deferred interest or Graduated Payment Mortgage (GPM).
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A loan repayment schedule in which the outstanding principal balance of the loan increases, rather than amortizing, because the scheduled monthly payments do not cover the full amount required to amortize the loan. The unpaid interest is added to the outstanding principal, to be repaid later.