As the New Zealand dollar approaches equality with the Australian dollar, the Bank of New Zealand says those anticipating a so-called "parity party" can hang on to their balloons.

The bank said in a commentary that the fundamental case for parity was poor, and that it expects the currency to oscillate around the low 0.90s over 2015.

"Parity party proponents are preparing to pop the Perignon," the bank said. The NZ/Australian cross rate hit a post-float high of A96.57c on Thursday, evoking more talk of possible parity with the Aussie.

The bank said the cross rate flirted with, or broke through, A95c, on five separate occasions. "None of these attempts came particularly close to knocking on parity's door," the bank said. "Quite simply, the fundamental factors that historically drive the cross do not support an attempt at 1.00."

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The differences between New Zealand and Australian interest rates, commodity prices and business confidence yesterday suggested the cross would be fairly valued around 0.91, it said.

"To justify parity in a fundamental sense, one would have to believe that the Reserve Bank will resume rate hikes in 2015 while the Reserve Bank of Australia cuts interest rates by 100 basis points, that milk prices near fully recover to all-time highs while iron prices resume their decline, and relative business confidence rises significantly beyond all-time highs.

"Just as the police can't break up every party, we can't know for sure that the parity party won't take place this time around."

The bank expects a return below A95c in the near term, targeting A90c by the year's end.