More than 65,000 Australians have breached their concessional superannuation contribution cap leading to additional (and possibly unnecessary) tax on their retirement funds.

According to Government figures, during the 2009-10 financial year, 65,733 people breached the concessional cap, compared to 28,291 the previous year.

The excess contributions cap was reduced from $50,000 to $25,000 for those aged under 50 in the 2009-10 financial year.  Amounts exceeding the cap are taxed at the highest marginal rate of 46.5% - an extra assessment of 31.5% on top of the 15% already paid by the fund.

For those aged over 50, the yearly cap was reduced from $100,000 to $50,000 in the 2009-10 financial year.