Inflation Erodes the Value of Cash
When savings account interest is 0.1% and the inflation rate is 2%, the real value of cash decreases by approximately 1.9% every year. A 1,000 man-yen savings deposit nominally grows to approximately 1,010 man-yen after 10 years, but in purchasing power terms it has declined to the equivalent of about 827 man-yen. In other words, the choice to "do nothing" is effectively paying a cost of approximately 19 man-yen per year.
Japan experienced prolonged deflation, which ingrained the perception that "cash is safe." However, since 2022, the inflation rate has been running at 2-4%. If this environment persists, the purchasing power of cash will erode by 20-30% over 10 years. Thinking of cash as a "zero-risk asset" is a misconception in an inflationary environment.
Purchasing Power Simulation by Inflation Rate
Let's see how the purchasing power of a 1,000 man-yen savings deposit (0.1% interest) changes under different inflation rates. At 1% inflation: purchasing power after 10 years is approximately 906 man-yen, after 20 years approximately 821 man-yen. At 2% inflation: after 10 years approximately 827 man-yen, after 20 years approximately 684 man-yen. At 3% inflation: after 10 years approximately 754 man-yen, after 20 years approximately 569 man-yen.
If 3% inflation persists for 20 years, approximately 431 man-yen of purchasing power is lost from a 1,000 man-yen deposit. This is an "invisible cost" that is difficult to notice because the nominal balance in your bankbook does not decrease. To preserve the real value of your assets, you need returns that exceed the inflation rate.
The Returns You Could Have Earned by Investing
If the 1,000 man-yen had been invested at 5% annual return instead of sitting in savings, it would have grown to approximately 1,629 man-yen after 10 years and approximately 2,653 man-yen after 20 years. The gap versus savings is approximately 619 man-yen after 10 years and approximately 1,643 man-yen after 20 years. This is the "opportunity cost of holding cash."
Of course, investing carries risk, and a 5% annual return is not guaranteed. However, the average return of global equity indices over the past 30 years has been around 7% per year, and there has been virtually no period of principal loss for holding periods of 15 years or more. Leaving funds that you will not need for the long term in savings deposits means you are taking the certain risk of inflation erosion. Books on inflation and asset protection provide concrete options for countering the erosion of cash value.
How to Think About the Right Cash Ratio
You should not reduce your cash to zero. An emergency fund (6-12 months of living expenses) and funds earmarked for use within 1-2 years should be kept in savings. Surplus funds beyond that should be invested according to your risk tolerance.
As a concrete guideline, if your monthly take-home pay is 30 man-yen, your emergency fund should be 180-360 man-yen. In addition, set aside cash for any large planned expenses within 1-2 years, such as a car purchase or travel. Any savings beyond that can be invested to reduce opportunity cost. Introductory books on asset management help you take the first step toward asset protection beyond relying solely on savings.
Next Steps - Put Your Surplus Cash to Work
First, subtract your emergency fund and any funds earmarked for near-term use from your current savings balance to calculate your surplus cash. If you have surplus cash, consider investing it in a global equity index fund through a NISA account. If a lump-sum investment feels uncomfortable, you can spread it out over 6-12 months through dollar-cost averaging.
Try our simulator to see the future asset value if you invest your current savings. Visualizing the "cost of doing nothing" in concrete numbers will clarify your motivation to start investing.