Why your retirement plan needs to be dynamic.

Every retirement calculator operates on the same basic premise — and as covered in the retirement number that actually matters, the way that number is expressed can be misleading before you've even started planning. You enter some information — your age, your income, your current savings, when you want to retire — and the calculator produces a result. A lump sum target. A monthly savings figure. Perhaps a projected KiwiSaver balance. You note the numbers, perhaps feel a little more informed than before, and move on.

Six months later, life has changed. Your investment returns were better than expected — or worse. You changed jobs. You had a child, or bought a house, or had a year where the savings target simply wasn't achievable. The numbers the calculator gave you are still sitting somewhere in your browser history, growing steadily less relevant.

This is the fundamental limitation of a one-off calculator — and it is why the distinction between a calculator and a dynamic retirement planning platform matters so much in practice.

The myth of the smooth path

Every retirement projection is built on assumptions. Investment returns are assumed to grow at a steady rate. Income is assumed to increase gradually. Contributions are assumed to be made consistently. The resulting projection shows a smooth, upward curve from today's savings balance to the retirement target — clean, predictable, and almost entirely unlike how financial life actually unfolds.

In reality, investment returns fluctuate — sometimes significantly. A strong year can put you meaningfully ahead of where the projection suggested you'd be. A poor year can do the opposite. Income changes when jobs change, when careers shift, when businesses go through difficult periods. Life events — a family, a house purchase, an illness, an unexpected opportunity — can dramatically alter the financial picture in either direction, sometimes very quickly.

None of this means retirement planning is futile. It means that a plan built once and never revisited is not really a plan at all. It is a projection — accurate at the moment it was made, and progressively less so as real life diverges from its assumptions.

What a dynamic plan looks like

A genuinely useful retirement plan does two things. First, it gives you a clear picture of your situation at a point in time — based on your actual current figures rather than estimates. Second, it allows you to update that picture regularly as your real situation changes, so the plan remains grounded in reality rather than in the assumptions made when you first set it up.

This is the thinking behind ThatDay's Update My Snapshot feature. Rather than treating a retirement plan as something you do once, ThatDay is designed to be returned to — periodically and whenever something significant changes. Users can update their actual investment balances, KiwiSaver contributions, and additional savings amounts to reflect where they genuinely are rather than where a set of initial assumptions suggested they would be.

When those figures are updated, ThatDay recalculates. The savings target adjusts to reflect the real current position. If investment returns have been stronger than assumed, the required monthly savings figure may drop. If a difficult year has left balances lower than expected, the plan will show clearly what is needed to get back on track. Either way, the user is working from an accurate picture rather than an increasingly outdated one.

A note on good years

There is one aspect of dynamic planning worth addressing directly. When investment returns are strong and ThatDay's updated snapshot shows a lower required savings contribution than before, it can be tempting to reduce savings to match the new, lower target.

ThatDay's view is that this is worth resisting where possible. The same market conditions that produce strong returns in good years produce poor returns in others — and a retirement plan that takes full advantage of the good years without building any buffer against the poor ones is more fragile than it needs to be. Where circumstances allow, maintaining a higher savings rate during good years is one of the most effective ways to hedge against the years when returns disappoint.

This is not a counsel of anxiety. It is simply an acknowledgement that smooth projections don't reflect smooth reality — and that the buffer created by saving a little more than the minimum required in strong years is genuinely valuable when conditions change.

The automatic update that keeps the plan current

One further feature of ThatDay's dynamic approach is worth noting. Each year on 1 January, ThatDay automatically updates users' desired retirement spending in line with its inflation assumptions. This means that even users who don't actively return to update their snapshot will find that one of the plan's core inputs — the retirement income they are working toward — remains current rather than silently drifting behind the real cost of living.

This matters because a retirement spending figure entered five years ago and never updated will understate what that lifestyle will actually cost by the time retirement arrives. The automatic annual update ensures the target stays honest without requiring the user to remember to adjust it manually.

Retirement planning as an ongoing relationship

The broader point is this: retirement planning is not an event. It is a practice — something that benefits from regular attention, honest updating, and a willingness to adjust when reality diverges from the plan. The New Zealanders who arrive at retirement most securely are rarely those who made a single perfect plan in their 40s and executed it without deviation. They are those who checked in regularly, updated their picture honestly, and made adjustments as their circumstances changed.

ThatDay is designed to support exactly this kind of dynamic, ongoing engagement with retirement planning. The retirement planning checklist for your 40s and 50s is a useful companion for anyone doing their first proper review.

Keep your plan current

ThatDay is a free retirement planning platform built for New Zealanders. Its Update My Snapshot feature lets you update your actual figures whenever your circumstances change — keeping your retirement plan grounded in reality rather than in assumptions made on a single day in the past.

Its financial assumptions were independently validated by the University of Auckland Business School's Master of Applied Finance programme.

Further reading: The retirement number that actually matters.

Keep your retirement plan current — start your free plan at thatday.co.nz