A Massey University-Westpac study shows the gap between national superannuation and the cost of a basic existence has widened with retirees needing to rely increasingly on private savings and investments.

A single person living in a major city on average spent $590.44 a week for a "no frills" lifestyle, which is $200 more than the superannuation payout. The figures relate to the year ended June 2017.

A couple living in the same way in a major city spent $872.22 a week compared to the $600.30 after tax super payout.

The cost of such a lifestyle in provincial areas was about $30 a week cheaper for a single person but by about $250 a week for a couple.

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