A sustained parity of the Australian dollar with the US dollar is likely to boost Australian banks' after-tax funding task by around $1 billion a year.That's the conclusion from Goldman Sachs estimates, published in its Daily Cable last week. The report said the higher $A would increase the funding task of the major banks by "$2 to $3 billion". The estimate was based on Goldman's revised $A target of $US1.05 by September 2011; the estimate was written with the $A at around $US0.97.The higher $A drives up bank funding costs by increasing the amount of foreign-denominated debt required to create a given amount of $A borrowings. The higher $A does not symmetrically increase the banks' ability to repay that debt, because the major banks hedge the vast majority of their foreign-denominated borrowings.      Goldman called the possible extra funding "a relatively small additional capacity requirement in light of the sector's $120bn-$140bn p.a. funding task." The increased funding task is not seen as a challenge. Market observers say the same economic strength that is supporting the $A is also making it easier for banks to borrow in overseas markets.A more accurate estimate of the rising $A's effect is almost impossible, requiring forecasts of bank asset growth, the term structure of borrowing, market lending rates and the mix between $US borrowing and borrowing in other currencies. Most of the $A's rise against the $US in recent months comes from the fall in the value of the $US. Against European and Asian currencies, the $A has risen only slightly.One guide is the data on cross-border claims published by the Bank for International Settlements.The BIS estimated cross-border claims by Australian banks at US$630 billion, of which more than half related to claims by European banks and less than a sixth related to claims by US banks.