Fannie Mae-No Politics (FNMA)

[capitalismforever]

would it not simply be 33.5B x (15%) v 33.b x (32.8%)

No. Deferred tax assets are $33.5b. They were calculated by using the effective tax rate of 32.8%. That means the amount the DTA derived from was $102.13b which is called the "book/tax difference". The next process is to take the book/tax difference (because that amount doesn't change) and apply the new 15% rate which will give you the new DTA value ($15.32b). The difference between the old DTA value and the new DTA value equals the impairment charge.