‘Subprime’ Mortgages Were Typically Both Adjustable-Rate (ARMs) and Interest-Only Mortgages with ‘Teaser’ Periods

‘Subprime’ mortgage loans are aimed by local brokers at families or neighbourhoods with poor or patchy credit histories. Just as jumbo mortgages are too big to qualify for Fannie Mae’s seal of approval (and implicit government guarantee), subprime mortgages are too risky. Yet it was precisely their riskiness that made them seem potentially lucrative to lenders. These were not the old thirty-year fixed-rate mortgages invented in the New Deal. On the contrary, a high proportion were adjustable-rate mortgages (ARMs) — in other words, the interest rate could vary according to changes in short-term lending rates. Many were also interest-only mortgages, without amortization (repayment of principal), even when the principal represented 100 per cent of the assessed value of the mortgaged property. And most had introductory ‘teaser’ periods, whereby the initial interest payments — usually for the first two years — were kept artificially low, back-loading the cost of the loan. All of these devices were intended to allow an immediate reduction in the debt-servicing costs of the borrower. But the small print of subprime contracts implied major gains for the lender. One particularly egregious subprime loan in Detroit carried an interest rate of 9.75 per cent for the first two years, but after that a margin of 9.125 percentage points over the benchmark short-term rate at which banks lend each other money: conventionally the London interbank offered rate (Libor). Even before the subprime crisis struck, that already stood above 5 per cent, implying a huge upward leap in interest payments in the third year of the loan.

—Niall Ferguson, The Ascent of Money: A Financial History of the World (New York: Penguin Press, 2008), 264-265.