The move will see NAB's cash earnings for the year ending 30 September 2014 slip by around 14 per cent to between $5.1 billion and $5.2 billion.
NAB chief executive Andrew Thorburn said the announcement of the writedowns was "disappointing".
A majority of the balance sheet adjustments relate to conduct charges within NAB's troubled UK banking operations.
Payment protection insurance provisions made up the bulk of the adjustments, representing AU$605 million after tax.
NAB has also been forced to provision AU$359 million in relation to its UK interest rate hedging products for the September 2014 half-year.
The bank has recorded a AU$220 million annual impairment charge of capitalised software following an assessment.
NAB has also taken a deferred tax asset provision in its New York branch of AU$132 million, and a research and development tax policy offset resulting in a AU$28 million cash earnings decrease.
The writedowns have all been 'taken above the line' on NAB's balance sheet to the approval of investment analysts who were briefed yesterday morning.
