Give them an inch and they'll take a mile.

That's basically the message to anyone worried about a capital gains tax in New Zealand.

In Canberra last night Jim Chalmers' budget was pitched as a 're-balancing' of 'intergenerational inequality'.

Fewer young people own homes in Australia, so they've pit grandkids against grandparents and made tax changes to negative gearing and capital gains.

Negative gearing is where landlords make a loss on their rental property - income (rents) are less than expenses.

They can claim the difference as a tax deduction on other income.

This, by the way, is something they said they wouldn't touch and now they have. Albanese and Chalmers ran an election campaign saying they wouldn't do this.

In the same way their Kiwi Labour colleagues claim their capital gains tax will be limited in scope and scale.

But what does it achieve?

The median cost of a Sydney house is AUD$1.7M. The country median is almost $1m.

That's more than Kiwi prices. Try buying a house in Melbourne - Godspeed.

The reason these changes are not going to change the game for any young Australian, or young Kiwi flying the coop, is simple: supply.

As anyone with a townhouse in West Auckland right now well knows, the faster way to lower prices is to build more of the things. Supply and demand.

And with these changes in Australia, fewer homes will be built, not more.

Master Builders Australia says the number of homes built in future as a direct result will go down.

In the Budget, Treasury, Chalmers' own Treasury, reckoned 35,000 fewer homes will be built over a decade.

Hardly a recipe for more affordable housing and 'intergenerational equality'.

See omnystudio.com/listener for privacy information.