Finally, an economist quantifies the effect of the sub-prime loans on foreclosures.

Dr. Cagan analyzed 8.4 million adjustable-rate loans made during those three years and estimated that 13% of them, totaling $326 billion, will end in foreclosures. After lenders resell those properties, the total losses for lenders or investors holding the loans will be $113 billion, he estimated. That is about 1% of total U.S. home-mortgage loans outstanding.

“The vast majority of borrowers will be fine,” Dr. Cagan said.

The estimates are based on an assumption that average home prices will remain about level with the December 2006 level over the next five years. If prices drop 10%, the number of foreclosures would jump to 1.9 million, Dr. Cagan projected. But a 10% rise in prices would cut foreclosures to 489,000, he estimated. When prices rise, people struggling with loan payments are more likely to be able to refinance into a loan with easier terms or sell their homes for more than the loan balance.

Dr Cagan adds that the worst-performing loans will be those that started with low “teaser” rates, below 4%. On such loans, the typical rise in monthly payments at the reset is 118%.