(Adds net interest margin, net profit, other bank results)
Nov 8 (Reuters) - Commonwealth Bank of Australia CBA.AX (CBA) said on Wednesday its first-quarter unaudited cash earnings grew 10.4 percent as a re-pricing of its mortgage book helped margins in its home lending division and impairment charges fell.
Cash earnings for Australia's biggest bank by market value came in at A$2.65 billion ($2.03 billion) for the three months ending Sept. 30, up from A$2.4 billion last year, the bank said in a limited trading update.
Bad debts fell to A$6.1 billion from A$6.8 billion a year ago.
Cash profit, a measure that excludes one-offs and non-cash accounting items, is closely watched by investors. On a statutory basis, net profit rose 16.7 percent to A$2.80 billion.
The bank said its net interest margin in the quarter improved, without providing a number.
It said the margin was helped by asset repricing but weighed down by a newly-introduced banking levy, higher funding costs and competition.
In March, CBA, like its three biggest rivals, said it would raise rates on interest-only and investment home loans, reacting to regulators' concerns that home prices in Sydney and Melbourne - Australia's two biggest cities - may be in a bubble. three other big banks - ANZ ANZ.AX , National Australia Bank NAB.AX , and Westpac Banking Corp WBC.AX - have reported a rise in full-year profit to September in the past two weeks. CBA's full-year reporting period is to the end of June.
CBA's common equity Tier-1 capital ratio at the end of September rose to 10.1 percent from 9.4 percent a year ago, below the Australian Prudential (LON:PRU) Regulation Authority's (APRA) target of at least 10.5 percent. impairment expenses edged down to A$198 million from A$322 million last year.
($1 = 1.3079 Australian dollars)