The Wizard first-home buyer index for May showed it now took 111.2% of one median income to pay the mortgage on the lower-quartile-priced house in May, up from 108.9% in April.
The index was 107% a year ago and 79.3% three years ago.
The largest deterioration in home affordability was in Queenstown, where the ratio worsened to 123.7% from 116.8% a month ago.
Essentially, the median income for a first-home buyer is not enough to buy a lower-priced house, with a deposit around 10% of the house's value.
However, a couple, or family, with more than one income might find the price affordable.
A first-home buyer is identified as an individual in the 25-29 age group who buys a lower-priced house.
The median weekly take-home pay for a first-home buyer was $593.72 in May, up from $591.98 in April and $568.41 in May last year.
By comparison, it took 104% of one median income for the 30-34 age group to pay the mortgage on the lower-priced house, up from April's 102%.
That index was 100% a year ago and 73% three years ago.
Wizard said a lower-quartile house was priced in May at $355,000, up 3.8% on April and 3.3% on May last year.
The median house price of $490,000 was up 7.9% on April and 1% on May last year.
A household that bought a Central Otago-Lakes district's median-priced house in May needed at least $1650.38 of weekly after-tax income for the mortgage to be "affordable".
A mortgage is affordable if the weekly payments are 40% of weekly take-home pay.
The latest figure is 8.5% more than the first-home buyer household required one year ago.
The news is not much better for first-home buyers in the rest of Otago, although the Central Otago-Lakes district is well out in front in the latest home affordability stakes.
In Otago, it took 52.3% of one median income to pay the mortgage on the lower-priced house in May, up from 50% in April.
The index was 54.8% a year ago and 40.5% three years ago.
Wizard puts the lower-quartile price for Otago at $180,000 (up 5.6% on April) and the median price at $240,000 (up 2.1%).
The median income for a first-home buyer is not high enough to buy a lower-priced house, with a deposit of around 10% of the house's value.
By comparison, it takes 49% of one median income for the 30-34 age group to pay the mortgage on a lower-priced house, up from 46.9% in April.
That index was 51.2% a year ago and 37.3% three years ago.
A household that bought Otago's median-priced house in May needed at least $775.74 of weekly after-tax income for the mortgage to be affordable, down 0.3% on what the first-home buyer required one year ago.
Across New Zealand, it took an average 70.6% of one median income to pay the mortgage on a lower-priced house which Wizard estimated cost $247,000.
The index was 73.4% a year ago and 48.1% three years ago.
The most affordable place to buy a first home was Southland.
