using conservative default rates of 40% on its $133 billion subprime book, 12.5% on its $314 billion of Alt-A mortgages and 4% on its remaining $2 trillion of prime home mortgages, Fannie could well be facing cumulative credit losses of over $50 billion. That’s after assuming Fannie will realize recoveries of 60% on its subprime and Alt-A loans and 70% on its prime loans.
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I believe the defaults rates will be much higher, especially on the prime mortgages — for sure higher than 4%