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The Government Superannuation Fund fell in value in January by 1.27% but still managed to return 19.33% on its nearly $25 billion in assets in the year ended January.
The fund, commonly known as the ''Cullen fund'', after its founder and former Labour finance minister Sir Michael Cullen, has returned 9.35% on average since its inception in 2003.
In the past five years, the return has been 16.24% and in the previous three years, the return has been nearly 14%.
The fund was established by Sir Michael to pre-fund the retirement payments to New Zealanders but the Government stopped paying into the scheme after the 2008 election.
Finance Minister Bill English indicated payments could restart when the Crown accounts return to surplus.
Because of the weighting to growth assets, the fund can experience large short-term movements.
But as a long-term investor, the fund has a greater-than-average ability to withstand the volatility.
The fund measures its performance in two ways: relative to the 90-day Treasury bill rate and relative to a passive reference portfolio benchmark.
Figures provided by the fund showed the reference portfolio fell 1.61% in the month and the Treasury bill rate had a 0.2% return in the month.
In the past 12 months, the reference portfolio grew by 14.62%, compared with the fund's 19.33%.
The fund expects to exceed the Treasury bill rate by at least 2.5% a year and has managed that since inception.
Since then, the fund guardians have added $8 billion to the fund compared with the Treasury bill rate.
Labour Party finance spokesman David Parker said without a long-term plan to gradually raise the retirement age to 67, National was risking a sudden increase in the eligibility age in the future.
''Australia is now openly considering raising the age to 70, following in the footsteps of the United Kingdom.
"New Zealanders don't want us to follow in the footsteps of those countries and nor does Labour.''
The Government's pretence the age of eligibility did not need to be increased looked increasingly dishonest, he said.
Labour's plan was to start gradually raising the super age to 67 by increasing the age by two months a year from 2020.
''That's a fair and reasonable way to ensure we can pay for our retirement. We will also have an exception for those who can't work past 65 in their normal job.''
Mr Parker said super costs had risen from $7.3 billion in 2008 to $10.2 billion at present.
That was already more than what was spent on all benefits combined, plus the accommodation supplement and working for families.