The partial sale of Kiwibank to the NZ Superannuation Fund and ACC has been completed with NZ Post netting $494 million from the deal.

The NZ Superannuation Fund will take a 25 per cent stake in the banks' holding company Kiwi Group Holdings Limited for $263m while ACC gets a 22 per cent holding for $231m.

"This is a big day for Kiwibank and - ultimately, for New Zealanders, who will retain 100 per cent ownership of a much stronger bank. Kiwibank now has access to new streams of capital and is positioned strongly to compete against the other major banks," said NZ Post chief executive Brian Roche.

The investors valued Kiwibank at $1.05 billion.

Mr Roche said NZ Post will reinvest $90m of the proceeds back into the bank.