The balance cannot fall, and that is exactly why the real risk in this class is invisible. Inflation reduces what the money buys, and the tax is levied on the nominal interest rather than on what you actually gained.
13 min read · Level 1
Cash is described as the safe asset, and the description is exactly half right in a way that does more damage than being wrong would. It is safe against the risk people can picture: the balance does not fall, no headline can take it away, and nothing needs watching. It is entirely exposed to the risk people cannot picture, which is that the number stays the same while what it buys does not. And because the visible risk is the one that generates fear and the invisible one generates nothing at all, the instrument attracts money in precisely the circumstances where it does most harm - after a frightening period in markets, held by somebody who has decided to be careful, for a horizon long enough that the subtraction compounds. I would put the sharpest version of it this way: a person who moved a large balance to cash during a bad year and left it there for a decade has chosen a certain loss of purchasing power in order to avoid an uncertain one, and has almost certainly not framed the decision that way, because nothing in the arrangement invites them to. The remedy is not to distrust cash. It is to compute the real, after-tax figure once a year and put it beside the balance, so that the two risks are both visible at the same time and the choice between them becomes a choice rather than an instinct.
This is the one class whose principal risk cannot be seen on a statement, because the statement shows a number that never goes down.
The balance is nominal. What matters is what it buys. Take an account paying 5.00% in a year when prices rise 6.20%:
Real return = (1 + 0.0500) / (1 + 0.0620) - 1 = -1.1299%
The balance grew. The purchasing power shrank. Nothing on the statement records the second fact, and there is no line anywhere that could.
Over five years on 30,000, with the same rates repeating:
Nominal value 30,000 x 1.05^5 = 38,288.45 In starting money 38,288.45 / 1.062^5 = 28,342.96 Real change -1,657.04, which is -5.5235%
Five years of a statement rising every month, ending 1,657.04 short of where it started in what it can buy. No decline was ever displayed. There was no bad day.
This is what distinguishes this class from every other risk in the curriculum. Elsewhere risk announces itself: a share falls, a building is revalued, a bond issuer defaults. Here it is a subtraction that is never printed.
And it does not require unusual inflation. With interest at 3.00% and inflation at 2.00%:
Real return = 1.03 / 1.02 - 1 = 0.9804%
Positive, and under one per cent a year. That is roughly the best this instrument offers in ordinary conditions, before any tax.
The other risks in this class are real and much smaller for most holders. Counterparty risk, which lesson one dealt with: below the guarantee limit it is a solved problem and above it, it is an ordinary credit exposure. And the risk of the rate being cut, which lesson two dealt with: the income can halve, the capital cannot.
There is no hidden cost layer here of the kind funds carry. Most savings accounts have no explicit charge. What this class has instead of fees is the spread from lesson three and the inflation subtraction above, and neither of them appears as a cost anywhere.
Because tax in this class is levied on the number that went up, not on what you actually gained, and that single fact makes the arithmetic worse in exactly the years it is already bad.
In the United States, interest credited on a bank deposit is generally treated as ordinary income and taxed in the year it is received, at the holder's ordinary rates. There is no deferral, because there is nothing unrealised: the interest is paid, so it is taxed. That is a different arrangement from an asset whose gain is untaxed until sale, and the difference compounds over long holds.
Take the earlier case and add a clearly illustrative 20% rate:
Interest on 30,000 at 5.00% 1,500.00 Tax at an illustrative 20% 300.00 After-tax interest 1,200.00, which is 4.00%
Real return before tax 1.05 / 1.062 - 1 = -1.1299% Real return after tax 1.04 / 1.062 - 1 = -2.0716%
Read those last two lines carefully. The saver's purchasing power fell, and they paid 300 of tax on the year in which it fell. The tax is computed on 1,500 of nominal interest; the real gain was negative. Nothing is malfunctioning - most tax systems are built on nominal amounts - and the consequence is that inflation and tax are not two separate subtractions but one compounding problem, worst precisely when inflation is highest.
Over the five years on 30,000, at 4.00% after tax:
Nominal value 30,000 x 1.04^5 = 36,499.59 In starting money 36,499.59 / 1.062^5 = 27,018.76 Real change -2,981.24, which is -9.9375%
Against -5.5235% before tax. Tax nearly doubled the real loss on an instrument whose entire purpose is safety.
Even the mild case narrows sharply. Interest 3.00%, inflation 2.00%, the same illustrative 20% rate: after-tax interest is 2.40%, and 1.024 / 1.02 - 1 = 0.3922% a year in real terms.
Three things generalise beyond any one country. Tax treatment of interest differs completely between jurisdictions - some allow an allowance of tax-free interest, some tax it at a separate rate, some at ordinary rates - and every one of those rules is revised by legislation. A tax-sheltered account, where one is available and not full, removes the charge entirely and is usually the largest single improvement available here. And the tax arrives annually whether or not the money was touched, which is why cash held in a taxable account for a decade is a decade of small annual charges rather than one at the end.
Every rate in this lesson is illustrative. Take the mechanism; never take the number.
This is educational information, not tax or accounting advice. Rules differ by country and change — get advice from a qualified professional in your jurisdiction before acting.
Educational, not personalised financial advice. Nothing in the Investor Academy is a recommendation to buy, sell or hold anything — what is right for you depends on your own circumstances and the rules where you live.
Sources: U.S. IRS - official tax information; U.S. SEC - Investor.gov; U.S. Federal Deposit Insurance Corporation; OECD - tax policy and statistics
The same 30,000, held for five years, in three arrangements. Inflation 6.20% throughout, and an illustrative 20% rate on interest.
Arrangement Nominal end In starting money Real change Taxable account at 5.00% 36,499.59 27,018.76 -9.9375% Sheltered account at 5.00% 38,288.45 28,342.96 -5.5235% Left in a current account at 0.00% 30,000.00 22,207.45 -25.9752%
Three observations, in order of how much they should change behaviour.
The third row is the largest number on the table and it is the one people do by default. Money sitting in a transaction account earning nothing lost 25.98% of its purchasing power across the period - 7,792.55 of what the money could buy - and the balance on the statement never moved. That is the single most expensive thing in this entire subject and it requires no decision to bring about.
The shelter is worth 4.414 percentage points of real outcome over the five years, being the gap between -9.9375% and -5.5235%. That is a bigger effect than any rate difference realistically available between accounts, and it is a question about the account type rather than about the bank.
The best available row still lost purchasing power. At 5.00% against 6.20% inflation, no amount of shopping around, splitting, or sheltering makes this instrument produce a real gain. That is not a failure of the saver. It is the instrument doing what it does, and the honest conclusion is that cash is the wrong place for money that has to grow - which is lesson six.
One clarification, because the table can be misread. None of these rows is a reason to avoid holding cash. The 30,000 was available in full, on any day, at a known amount, throughout. That is what was bought, and for money with a job that requires those properties it is worth paying for. The error is not holding cash. The error is holding cash for a purpose that needed growth, or holding it at 0.00% when 5.00% was available for the same money with the same access.
Reading a rising balance as a gain. At 5.00% interest against 6.20% inflation the real return was -1.1299%, and the statement displayed an increase every month. This is the only class in the curriculum where the risk is invisible by construction.
Leaving money in a transaction account because it is convenient. On the table above that cost 25.98% of purchasing power over five years - the largest single figure in this subject - and it is the arrangement that requires no decision at all.
Applying one rate to a return that has not been adjusted for inflation. Tax is computed on nominal interest, so in a high-inflation year a saver pays on a gain they did not make in real terms. Inflation and tax are one compounding problem here, not two separate ones.
Ignoring the account type because it feels administrative. The shelter was worth 4.414 percentage points of real outcome across five years, which is larger than any realistic difference between two banks' rates.
Concluding that cash should be avoided. The 30,000 was available in full on any day at a known amount throughout, and that is a genuine and sometimes essential property. The conclusion is about matching the instrument to the job, which lesson six sets out.
Assuming interest is taxed the same way everywhere. Some jurisdictions give an allowance of tax-free interest, some apply a separate rate, some tax it as ordinary income - and all of them revise the rules.
Divide one plus your rate by one plus the inflation rate and subtract one. At 5.00% against 6.20% that is -1.1299%. It is one calculation, it is the only figure in this class that describes what is actually happening, and no statement will ever show it to you.
Reduce the rate by whatever charge applies to interest in your jurisdiction and repeat. In the worked case 5.00% became 4.00% and the real return went from -1.1299% to -2.0716%. Doing both is what shows that tax and inflation compound rather than adding.
Transaction accounts, dormant accounts, platform cash balances, money left over from something. This is the highest-value action in the subject: the 0.00% row lost 25.98% of purchasing power across five years, and correcting it needs no view about anything.
Where such an account exists in your jurisdiction and has room, the same money in it is a materially different proposition - 4.414 percentage points of real outcome across the worked five years. This is a question about the account rather than the bank, and it is the point at which to take advice for your own country rather than reasoning from a lesson.
Once the real, after-tax figure is in front of you, ask what job the money is doing. Money with a date and a required amount belongs here even at a negative real return. Money that has to grow does not, and no amount of optimising within this class changes that - which is the whole of the next lesson.
Once a year on every cash balance, whenever inflation moves materially, when deciding between a taxable and a sheltered account, and before concluding that a large cash balance is a conservative position.
Do not apply any tax figure in this lesson to your own position - every one is illustrative and no country's system works exactly this way. And do not use a negative real return as a reason to move money that has a fixed date and a required amount; certainty is what that money is paying for.
Households frequently hold a substantial cash balance across many years without reviewing it, because nothing about it ever prompts a review. The statement rises, no charge appears, no market news concerns it, and the account requires nothing. Over a decade of ordinary inflation the purchasing power of that balance declines materially while the displayed figure only grows, and the erosion is never experienced as an event. When it is eventually noticed, it is usually because the money is being spent on something whose price is now visibly higher than expected, and the realisation arrives as a surprise about the cost of the thing rather than as a fact about the account.
A balance that has not been reviewed in years is not dormant, it is shrinking. Write the real return beside the balance once a year so the subtraction is on the page.
Tax systems are generally built on nominal amounts, so interest is taxable in full regardless of what inflation did over the same period. In years when rates and inflation are both high, this produces the counter-intuitive combination of a larger tax charge than usual on a holding whose real value declined - the saver receives more interest, pays more tax on it, and ends the year able to buy less than at the start. Nothing is malfunctioning and no rule has been misapplied; the charge follows directly from taxing the nominal figure. It is nonetheless the point at which the arithmetic of holding cash through an inflationary period is least intuitive and most worth writing out.
Compute the real return after tax, not before. In a high-inflation year the two subtractions compound, and the tax charge is largest exactly when the real outcome is worst.
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