Economists are baffled over BNZ's decision to bump up the interest rates on three home loan terms.

The bank will lift their six-month rate from 7.85 percent to 7.99 percent. Their four- and five-year rates will increase from 6.89 percent to 7.09 percent.

Infometrics Chief Forecaster Gareth Kiernan says the six-month rate increase is at odds with BNZ's own economic forecast.

"The six-month rate is out of line with all the other banks, it's higher than the other banks are offering. So it's hard to see, unless they're trying to funnel more of the lending out towards the longer end."

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