(Reuters) -Commonwealth Bank of Australia ( CBAUF ) reported better-than-expected first-half cash earnings on Wednesday, helped by robust volume growth across its home lending and deposit products portfolio as well as a lower loan impairment expense.

The country's biggest lender said its cash net profit after tax was A$5.13 billion ($3.23 billion) for the six months ended December 31, compared with A$5.02 billion a year earlier, and beating a Visible Alpha consensus estimate of A$5.06 billion.

CBA's net interest margin, a key profitability metric defined as the gap between loan interest and the interest paid to depositors, rose 2 basis points from last year to 2.08%.

CBA said the effects of competitive pressure on deposits and lending pricing were offset by higher earnings on capital hedges and the replicating portfolio.

It declared an interim dividend of A$2.25 per share, compared with A$2.15 apiece last year.

($1 = 1.5888 Australian dollars)