How big is the bad or “toxic” mortgage and loan problem in the US? Nouriel Roubini says the total losses on US mortgages and loans will be 3.6 Trillion, while the IMF has a lower estimate at 2.2 Trillion. Is there an easy way to gauge the size of this problem and check the veracity of these estimates?

Total US mortgage debt outstanding, including residential, commercial, and farm properties, stood at $14.7 Trillion dollars in December 2008. Of this, $4.9 Trillion in residential mortgage debt is guaranteed by the federal government through Fannie Mae, Freddie Mac, and Ginnie Mae, and does not expose holders of this debt to any risk of loss.

During the depths of the Great Depression, roughly half of all mortgages on homes in major cities were in default. Interestingly, home prices only fell by 20% during the same period, so that even during the Depression, banks could expect to eventually recover 80% of the value of their defaulted loans – and this is assuming 100% financing!

Housing prices are falling more sharply in the current downturn, with Economy.com predicting a peak-to-trough decline of 36%. Mortgage default rates so far have been much lower than the Great Depression, and total defaults across all mortgages are unlikely to exceed 20% during this recession. Assuming a hefty 20% default rate, and an extraordinary 50% drop in home values, banks would still lose only 10% of total loan principal. This would amount to a worst-case $1 Trillion loss in US mortgage lending. According the Federal Reserve, consumer and commercial loans together total another $4 Trillion in principal outstanding. If these loans default at a high rate of 25%, another $1 Trillion in losses would be incurred, for a total of $2 Trillion in US loan losses.

These simple calculations take into account the extraordinary default rates and real estate price drops occurring today, and yet the $2 Trillion in projected losses and is far lower than some economists’ estimates. Perhaps the problem is more tractable than suggested; while $2T is a large sum, it’s much more manageable than the $3-4T predicted by pessimists!