Why Cash "Under the Mattress" Loses Value Every Year

There is something reassuring about cash. You hold it, you see it, no one can "go bankrupt" on you with it, there is no app to show you a red number on a bad day. That is why so many people keep significant sums in cash at home or in a current account with almost zero interest — "under the mattress," as the saying goes.

But this is exactly where one of the most expensive illusions in personal finance hides: safe does not mean preserved. The number on the banknotes really does not change — €10,000 today is €10,000 10 years from now too. What quietly changes is how much you can buy with it. In this article you will see exactly how much inflation "eats" from cash over time, why even a low-interest deposit often loses too — and in which cases cash is nonetheless the right choice.

"Safe" does not mean "preserved"

Inflation works like an invisible tax on money at rest. It does not take banknotes out of your wallet — it leaves them untouched, but makes each of them a little more powerless every year.

At a sustained inflation of 4%, a basket of goods that costs €100 today costs €104 next year. Your €100 in cash has not grown — so it now buys less. A single year is imperceptible. The problem is that the years pile up, and multiplicatively: the second percent is charged on the already higher prices, the third on the higher still. This is compound interest, but turned against you.

Why the loss is invisible

If someone pulled €30 out of your wallet, you would feel it at once. Inflation does the same, but in a way the brain struggles to register, because it lacks all the usual signals of a loss:

• There is no transaction. You see no withdrawal, no text message arrives. The number in the account stays the same or even grows.
• It happens slowly. 4% over a year, spread across the days, is below the threshold of the noticeable.
• You compare against the wrong baseline. You remember the price from a year ago, rarely from ten years ago — so you underestimate the accumulated effect.

It is exactly this invisibility that makes cash "under the mattress" so insidious: no one attacks you, it simply waits for you to do nothing for long enough.

How much inflation eats: 5, 10 and 20 years

Let's put numbers to it. Here is what remains of the purchasing power of €10,000 held in pure cash (zero interest), at a hypothetical sustained inflation of 4% — this is pure arithmetic, not a forecast:

Read the last row slowly: after 20 years the same banknotes buy about less than half of what they buy today. You have spent nothing, no one has robbed you — you have simply kept value where it quietly melts away.

Compute your own case with the real-return calculator. Enter a nominal return of 0% (that is cash) and your expected inflation — the calculator shows the real value in today's money and warns you when it falls. Switch the period to 20 years to feel the difference.

A low-interest deposit often loses too

"All right — I'll put it in a deposit, at least there's interest there." A reasonable step, but with a caveat: what matters is not the interest by itself, but the interest minus inflation. If the deposit pays less than prices rise, you still lose in real terms — just a little more slowly than cash.

Here are the three typical cases at a hypothetical inflation of 4% over 10 years:

The deposit at 2% interest with inflation at 4% still loses purchasing power — the real return is about −1.9% per year. Only when the interest matches inflation do you simply preserve value (real return ≈ 0%), without gaining.

Stretch the same deposit over 20 years and the picture becomes even clearer: nominally the account grows to about €14,859, but in real terms it buys as much as €6,782 today — a loss of about 32%, the same as pure cash over 10 years. A low interest rate does not stop the loss, it only slows it. Try the scenario in the calculator, and for a detailed comparison see Deposit vs investing over 10 years.

When cash is nonetheless the right choice

So far it sounds as if cash is the enemy. It is not — it just has a precisely defined job, and that job is not "long-term wealth accumulation."

Cash and a liquid deposit are the right choice for:

• An emergency fund. The money for 3–6 months of expenses must be liquid and safe, even at the cost of a small real loss. Its job is to be there the moment it is needed — not to grow.
• Money for a near-term goal. If in 1–2 years you need a sum for a specific purpose (a car, a renovation, tuition), the volatility of the markets is a bigger risk than inflation over such a short horizon.
• Peace of mind. Having a buffer that does not wobble has real psychological value. It guards against the panicky decisions that cost the most.

In other words: the small real loss on your emergency fund is the price of the insurance, not a mistake. The problem begins when money whose job is to grow for decades lies under the mattress.

The key word is horizon. For money you will need soon, safety is worth more than the small inflationary loss — here cash wins. For money with a horizon of decades the opposite holds: there, slow erosion, not market swings, becomes the biggest risk.

What follows from this

The takeaway is not "spend everything" and not "put everything in the market." The takeaway is to answer one question for every sum of money you hold: is this sum being preserved, or should it grow?

• If it is being preserved (emergency fund, near-term goals) — liquidity and safety win, cash is in its place.
• If it should grow (retirement, long-term wealth) — the goal is a real return above inflation, and that has historically come from investing, not from cash.

That is exactly why real return, not the nominal number, is the compass. For historical context on why this matters especially here, see Inflation in Bulgaria.

Sources

• The National Statistical Institute (NSI) — the official inflation data (CPI/HICP) that determines how much the basket "rises in price": nsi.bg (opens in new tab)

The figures in the tables are arithmetic illustrations under an assumed sustained inflation, not a forecast — real inflation changes every year.

Continue reading

• Inflation and real return — how to compute purchasing power with the formula.
• Inflation in Bulgaria: a historical look — why cash suffers most in the loud years.
• Deposit vs investing over 10 years — the same contribution at a deposit rate and at a market return.
• Investing for beginners — the first steps, if you decide that part of your money should grow.

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