In 2024, 2.9 million New Zealanders sit in the 40-44 age bracket. That's 147,000 more than last year. It's the single biggest one-year jump this cohort has seen since 2000.

Here's the tension: this is meant to be when your career peaks. When the promotions land. When the salary finally reflects the two decades you've put in. The 40-44 bracket should be a gold mine for tax revenue, a cohort hitting their stride.

But look at what happens next in the data. These people are about to turn 45. And when you track what happened to previous cohorts as they crossed that threshold, the taxable income story gets complicated fast.

The 40-44s grew by just 80,000 people between 2020 and 2023. Then 147,000 arrived in one year. That's not gradual demographic change. That's a bulge. And it's hitting right now.

This matters because New Zealand's tax system runs on the assumption that people in their forties are earning serious money. They're meant to be carrying the load while younger workers find their feet and older workers wind down. But the trajectory of this group tells you something's off.

Between 2000 and 2024, the 40-44 age group grew by 450,000 people. That's a 56% increase over 24 years. Compare that to the relatively stable growth in other brackets, and you see the pressure point: a massive cohort, all aging at once, all expecting their peak earning years to deliver.

What they're walking into instead is a labour market where seniority doesn't guarantee much anymore. Where restructures hit the expensive employees first. Where being 45 with a mortgage and kids and aging parents makes you expensive, not valuable.

The 2024 spike is particularly stark. From 2.75 million to 2.89 million in twelve months. That's equivalent to adding the entire population of Wellington to this single age bracket. And every one of them is carrying the financial weight that comes with mid-life: mortgages, school fees, elderly parents needing care, KiwiSaver contributions they should be maximizing but probably aren't.

The data doesn't tell you what happens to individual tax returns as people age. But it does tell you this: a huge wave of workers just hit the age where they're supposed to be at their most economically productive. And the economy they're entering is very different to the one that rewarded their predecessors.

In 2020, when this group was smaller and the economy was about to shut down, there were 2.57 million of them. Four years later, despite COVID, despite inflation, despite everything, another 320,000 joined them. (Source: Stats NZ, taxable-income-sources)

They're here. They're mid-career. And the numbers suggest what comes next might not be what they planned for.