Interest and indexation of your HELP debt
There is no real interest charged on your HELP debt. Your accumulated HELP debt is indexed annually to reflect changes in the Consumer Price Index (CPI).
The indexation adjustment is made by the ATO on 1 June each year and applies to the portion of debt which has remained unpaid for 11 months or more.
On 1 June each year, all unpaid debts incurred between January and June of the previous year will be indexed and become part of your accumulated HELP debt. Debts incurred between July and December of the previous year will also become part of your accumulated HELP debt but will not be indexed until 1 June of the following year.
The current indexation rate may be found on the ATO website at:
Australian Taxation Office HELP Indexation Rates 2006-onwards
Australian Taxation Office HECS Indexation Rates 1990-2005 
See also:
Loans