Is Cash Really Trash? When to Hold and When to Invest

Interest rates may have changed, but too many savers haven't changed with them.

It's a mantra ingrained from childhood: save money, be frugal, keep a rainy-day fund. For generations of New Zealanders, depositing cash in a savings account or term deposit was the bedrock of financial prudence. Simple, low-risk, and guaranteed.

For anyone looking to genuinely build or preserve wealth, though, this old wisdom has become expensive. Holding significant cash beyond your emergency fund is no longer a conservative approach. It is a near-guaranteed loss of purchasing power. The mantra "cash is king" has been quietly replaced by a more uncomfortable truth: for long-term wealth building, cash is trash.

Twenty or more years ago, a New Zealander could park money in a term deposit and earn a meaningful return above inflation. Those days are gone. Interest rates have structurally shifted lower, yet many people continue to treat savings accounts and term deposits as a genuine wealth-building tool. The gap between what savers expect and what cash actually delivers has never been wider.

Banked Cash And The Arithmetic Your Bank Statement Doesn't Show

The interest rate printed on your bank statement is a feel-good number. What actually matters is the real return you receive after two relentless, wealth-eroding forces are applied: tax and inflation.

Let's use New Zealand figures as at July 2026 to illustrate the point.

The Official Cash Rate (OCR) sits at 2.50 percent as at July 2026, following the Reserve Bank's first increase since May 2023. A 12-month term deposit at a major bank pays roughly 3.5 to 4.0 percent. Annual inflation, measured by the June 2026 quarter CPI, came in at 4.1 percent.

Now, assume you have $100,000 on a 12-month term deposit paying 4 percent (a generous assumption at most banks). Here's what actually happens to your money:

• Gross interest earned: $4,000
• Tax at 33 percent (the marginal rate for most middle- and upper-income earners): $1,320
• After-tax interest: $2,680
• Purchasing power lost to inflation at 4.1 percent: $4,100
• Your real return: negative $1,420, or roughly -1.4 percent

Read it again: you locked your money away for a full year and ended up poorer in real terms. Your bank statement says you earned $2,680. In truth, you lost ground.

Some savers use PIE (Portfolio Investment Entity) term deposits, where tax is capped at 28 percent rather than 33 percent. This improves the after-tax return slightly, to about $2,880, but the real return is still negative after inflation. The tax structure doesn't change the fundamental problem.

Even at the best available 12-month rate in the market (3.95 percent as at late July 2026), the after-tax return of about 2.6 percent falls well short of 4.1 percent inflation. All the effort of locking money away for 12 months, and you still lose ground.

"…the arithmetic makes it plain that inflation is a far more devastating tax than anything that has been enacted by our legislature [government]. The inflation tax has a fantastic ability to simply consume capital. It makes no difference to a widow with her savings in a five percent passbook account [savings account] whether she pays 100 percent income tax on her interest income during a period of zero inflation or pays no income taxes during years of five percent inflation. Either way, she is 'taxed' in a manner that leaves her no real income whatsoever. Any money she spends comes right out of capital. She would find outrageous a 120 percent income tax, but doesn't seem to notice that five percent inflation is the economic equivalent."

Warren Buffett

As the Oracle of Omaha points out, the government doesn't need to explicitly charge you a wealth tax; the currency does the job quietly, efficiently, and legally. If only the IRD sent you an annual statement showing the "inflation tax" you'd paid, people might treat cash with an appropriate level of scepticism.

Learn more: The tax on inflation | The single tax | What is the Reserve Bank of New Zealand?

Five Years of Erosion

Over the five years from early 2020 to early 2025, the RBNZ's own inflation data shows the purchasing power of the New Zealand dollar fell by roughly 19 percent. In practical terms, $100 in 2025 buys about what $81 did in 2020. This erosion reflects cumulative price rises across the economy, and it underscores how persistently elevated inflation chips away at real savings over time.

Much of this was driven by the post-pandemic period. Central banks the world over deployed massive quantitative easing programmes, flooding economies with new currency to avert economic collapse. They didn't burn your cash. They created a lot more of it, and every existing dollar was forced to compete with the new arrivals.

The OCR was cut nine times between August 2024 and late 2025, then the Reserve Bank lifted it to 2.50 percent in July 2026, with further rises signalled. The direction matters less than savers hope: term deposit rates follow the OCR both ways, but tax and inflation apply regardless, and with annual inflation at 4.1 percent even improving nominal rates leave cash going backwards in real terms.

So What Should You Do Instead of Save?

It helps to draw a clear line between savings and capital. Savings are money set aside for spending: bills, emergencies, a car, a house deposit top-up. Cash is the right home for these funds. Capital is money intended to grow over years or decades. Leaving capital sitting in cash is where the damage occurs.

If cash is the long-term loser for capital, the answer lies in putting it to work across a broader range of assets. Professionals typically classify investments into four broad groups: cash, bonds, property, and shares. Cash has its place for liquidity and short-term needs. The other three are where long-term wealth is built.

1. ‍Bonds provide stability and income. They act as ballast in a diversified portfolio, often holding value or appreciating when growth assets fall. Most New Zealanders own bonds indirectly through funds such as KiwiSaver, particularly in conservative or moderate fund choices.‍
2. Property investment offers capital appreciation, rental income, and a natural inflation hedge. As building costs and labour prices rise, so does the replacement cost of existing property. When purchased with debt, property can deliver a double return: the asset appreciates while the mortgage is simultaneously devalued in real terms by inflation.‍
3. Shares (also called equities or stocks) have historically delivered the highest long-term returns of any asset class, averaging 7 to 10 percent annually over decades. Unlike a term deposit, a well-run company can raise its prices to offset inflation. Economists call this pricing power, and it is the core reason businesses outperform cash over time. A term deposit has zero pricing power; its value is simply determined by its denomination.

The critical point is not to abandon cash entirely but to hold only what you need for liquidity, your emergency fund, and any spending goals within the next 12 to 24 months. Everything beyond this should be working harder inside a well-diversified investment portfolio designed to deliver positive real returns after tax.

Whether you are 30 or 65, the long-term goal remains the same: ensure the weighted, after-tax, expected return of your overall portfolio substantially exceeds the rate of inflation. This typically requires clear financial planning, a robust understanding of market cycles, and disciplined execution.

How Do Interest Rate Changes Affect You?

The two most obvious effects run through mortgage repayments and savings returns. When rates fall, borrowers get relief and savers earn less. When rates rise, as they began to in July 2026, repayments climb and nominal deposit returns improve. In both directions we see more people seeking help: borrowers looking to restructure, and savers realising that even improved rates leave their cash trailing inflation after tax.

If you're holding significant savings in the bank and are serious about protecting your purchasing power, the team at Become Wealth can help. We assist individuals and families with these decisions every day. Book a complimentary, confidential initial consultation and let's look at your situation together.

Frequently Asked Questions

Is keeping cash in the bank a bad idea?

Not entirely. Cash is essential for day-to-day expenses, an emergency fund covering three to six months of living costs, and any specific purchases planned within the next one to two years. Beyond these needs, holding large amounts of cash long-term is likely to result in a negative real return once tax and inflation are accounted for.

What is a "real return"?

A real return is the gain (or loss) on an investment after adjusting for inflation. If your term deposit earns 4 percent but annual inflation is 4.1 percent (as at the June 2026 quarter) and you pay 33 percent tax on the interest, your real return is negative. Your money buys less at the end of the year than it did at the start.

What are the four main asset classes?

The four traditional asset classes are cash, bonds (fixed interest), property (real assets), and shares (equities). Each carries different levels of risk and expected return. A well-diversified portfolio typically includes a mix of all four, weighted according to your goals, time horizon, and risk tolerance.

How does inflation erode savings?

Inflation means prices rise over time. If your savings earn less than the rate of inflation after tax, your purchasing power declines even though the dollar figure in your account grows. Over five years of persistent inflation, the cumulative effect can be substantial. Between 2020 and 2025, the New Zealand dollar lost roughly 19 percent of its purchasing power.

Should I move all my savings into shares?

No. Every person's situation is different, and the right mix of assets depends on your age, goals, income needs, and tolerance for short-term volatility. Shares offer the highest long-term returns but can fluctuate significantly in the short-term. A financial adviser can help you determine the right balance for your circumstances.

What is the current OCR and why does it matter?

As at July 2026, the OCR is 2.50 percent, following the Reserve Bank's first increase since May 2023, with further rises signalled. The OCR influences the interest rates banks offer on savings and charge on loans. Term deposit rates broadly track it in both directions, but the return that matters is what remains after tax and inflation, and for cash that figure is typically thin or negative.