Bank of America and Wall Street firms that notched perfect trading records in the first quarter are now depending on an accounting benefit last used in the depths of the credit crisis to prop up their results. Bank of America, the biggest US bank by assets, may record a $1bn second-quarter gain from writing down its debts to their market value, Citigroup analyst Keith Horowitz estimated in a June 23 report. The boost to earnings, stemming from an accounting rule that allows banks to book profits when the value of their own bonds falls, probably represented a fifth of pretax income, Horowitz wrote.