Introduction
“Time deposit at 0.3% per year,” “variable mortgage rate of 0.5%,” “government bond yield of 1.5%” — every rate you see on a screen is a nominal interest rate. But two products with the same nominal rate can have completely different real value, depending on whether prices are rising or falling.
This article explains the difference between nominal and real interest rates with formulas and concrete examples, and shows how knowing this difference actually helps your household and business decisions. It is based on Microfund’s ongoing observation of interest rates and inflation, and on publicly available statistics, as of May 2026.
What You’ll Learn
- The relationship between nominal rate, real rate, and expected inflation (Fisher equation)
- Why the same “1% per year” deposit can be a gain or a loss depending on inflation
- Four situations where the real rate matters: savings, investing, borrowing, and reading the economy
- Real-world patterns of people who used the real rate well — and those who got burned by ignoring it
Who This Article Is For
This article is written with the following readers in mind:
- People who only vaguely sense that inflation “eats away” at their savings
- People deciding between a fixed and variable mortgage who want a clear framework
- Investors who don’t want to be misled by headline yields
- Business owners using debt who want to assess the “real burden” of repayments
- Anyone who wants to understand BoJ or Fed news in their own words
Rather than a textbook treatment, the goal is the minimum interest-rate literacy needed to avoid common mistakes in everyday decisions.
What Is the Nominal Interest Rate?
The nominal interest rate is the rate you see on a passbook, loan contract, or bond yield table — the “face value” rate, with no adjustment for changes in prices.
For example, depositing 1,000,000 JPY at 1% per year gives you a balance of 1,010,000 JPY a year later. The number on the screen has gone up by 10,000 JPY. So far, so easy.
What Is the Real Interest Rate?
The real interest rate is the nominal rate adjusted for inflation. It tells you how much your purchasing power has actually changed.
Suppose prices rose by 3% during that year. Your balance is now 1,010,000 JPY, but the basket of goods that cost 1,000,000 JPY a year ago now costs 1,030,000 JPY. On paper you gained 10,000 JPY, but in real terms you lost about 20,000 JPY of purchasing power. The real interest rate in this case is roughly -2%.
The Fisher Equation
The relationship between nominal rate, real rate, and expected inflation is captured by Irving Fisher’s well-known approximation:
Nominal ≈ Real + Expected Inflation
Rearranged for everyday use:
Real ≈ Nominal − Expected Inflation
The exact formula is slightly more complex, but for practical decisions, this simple subtraction is enough.
The Same 1% Means Different Things
“Time deposit, 1% a year” sounds the same in any environment, but the real meaning depends entirely on inflation at the time.
In Case A, your purchasing power genuinely grows. In Case C, despite earning interest, you are losing real value every year. If you only look at the nominal rate, you can quietly lose wealth without noticing.
Four Situations Where It Pays to Know This
1. Savings — Are you really accumulating wealth?
As of May 2026, ordinary deposit rates at most Japanese banks are still in the 0.001%–0.2% range, while the consumer price index is rising around 2% year-on-year. That means the real rate on deposits is in negative territory. “Money in the bank is safe” is true at a nominal level, but in purchasing-power terms it is being slowly eroded. Even understanding this much makes you stop and reconsider holding all your cash in a single ordinary deposit account.
2. Investing — Compare expected returns on a real basis
Long-term equity returns, real-estate yields, and bond coupons should all be compared on a real basis to be meaningful. If you compare “5% gross rental yield” with “7% return on US equities” without subtracting the relevant inflation rates, you are not comparing the same thing. Using the real rate as a common ruler protects you from being seduced by headline “high yields” in sales material.
3. Borrowing — See the real cost of repayments
When taking out a mortgage or business loan, it is natural to focus only on the nominal rate. But if inflation continues and your income or revenue rises in nominal terms, the real burden of fixed nominal repayments shrinks over time. In a deflationary environment, the opposite is true: a long-term fixed loan grows heavier in real terms. Decisions like “borrow now or wait,” “fixed or variable,” become much sharper when you think in real-rate terms.
4. Reading the economy — Understand central bank moves
When the BoJ or Fed raises or cuts rates, what they care about is the real rate, not the nominal one. “We’ve raised the policy rate to 2%, but with inflation at 3%, the real rate is still negative — policy remains accommodative.” Once you grasp the real-rate idea, that kind of statement becomes immediately meaningful, and economic news gains a new layer of resolution.
Does Inflation Make Debt Heavier or Lighter?
Bottom line: debt fixed in nominal terms gets lighter in real terms as inflation rises. Under deflation, the opposite happens — the same fixed debt grows heavier in real terms.
The reason is simple. Your loan balance and interest payments are fixed at contract values, but as prices and wages rise, the share of your income or revenue needed to cover those same nominal payments shrinks. Debt is fixed in nominal terms; income tends to grow in nominal terms — this asymmetry is what favors borrowers during inflationary periods.
A concrete example: a 30M JPY mortgage at 1% fixed
- At signing, annual income is 5M JPY — repayment feels significant.
- After 10 years of 2% annual inflation in both prices and wages, income is about 6.1M JPY. The repayment amount hasn’t changed, so its share of income falls naturally.
- In a deflationary scenario where wages decline, the real burden of the same repayment grows heavier year by year.
Same idea, via the real rate
This shows up directly in the real-rate formula:
Real Rate ≈ Nominal Rate − Inflation Rate
If you locked in 1% fixed but inflation runs at 3%, the real rate is −2%. In purchasing-power terms, despite paying interest, you are effectively “earning” about 2% per year by holding the debt. Historically, generations who took out long-term fixed mortgages early in inflationary periods have benefited substantially. The mirror image — locking in a fixed rate during deflation — leaves borrowers carrying heavier real burdens for years.
Important caveats
“Inflation makes debt lighter” depends on several conditions. It doesn’t apply automatically to every borrower:
- Your income must rise with inflation: If wages don’t keep up, if you live primarily on a fixed pension, or if your business prices can’t track inflation, the benefit is muted.
- Variable-rate loans see limited benefit: When rates reset upward with inflation, the “negative real rate” window doesn’t last. To capture the full inflation-erosion effect on debt, long-term fixed-rate borrowing is the relevant structure.
- Cashflow must hold up: If income drops to the point where you cannot make payments, the real-rate argument is moot — the immediate problem is solvency, not the long-term real burden.
- Bad news for savers and bondholders: The same inflation that helps fixed-rate borrowers erodes the real value of cash, deposits, and fixed-coupon bonds. Understanding this symmetry — borrowers gain, savers and creditors lose — helps you make a more coherent asset-allocation decision.
Patterns That Worked
Among the people Microfund has observed, those who acted with the real rate in mind have come out noticeably better. (Patterns are summarized rather than naming individuals or firms.)
- Partial shift to real assets during inflation: When real deposit rates went deeply negative, some households kept their emergency cash buffer in deposits but moved part of their surplus into equity index funds and real estate. Reframing “holding all cash” as itself a risk preserved their purchasing power.
- Long-term fixed mortgage at a historically low real rate: People who locked in a long-term fixed mortgage when real rates were unusually low later benefited as inflation rose. Their decision criterion was not “the headline rate is low” but “the real rate is low,” which made all the difference.
- Well-timed business borrowing: Business owners whose revenues were likely to rise with prices took advantage of low real rates to finance equipment investment. With repayments fixed in nominal terms, rising inflation effectively reduces the real repayment burden over time. A solid business plan is the foundation, but the habit of viewing rates relative to inflation drove better timing.
Patterns That Didn’t Work
- Chasing high “nominal” yields in foreign currencies: Some savers moved into emerging-market currencies attracted by 10%+ nominal rates, only to find local inflation higher still and the currency itself depreciating. In yen terms, the loss was significant. The lesson: high-yield currencies usually come with high inflation, too.
- Long-term fixed loans during deflation: When prices and wages were falling, taking out a long-term fixed-rate loan left borrowers with payments that grew heavier in real terms year by year. Thinking in real-rate terms would have prompted earlier consideration of switching to a variable rate or accelerating prepayments.
- “My savings are safe” — for decades: People who kept all their wealth in ordinary deposits over many years woke up to find that what once cost 10 million yen now cost 12 or 13 million. Their balance grew, but the goods it could buy barely did. This is the textbook outcome of long-term real-negative rates.
- Buying products by headline yield only: Buyers who took “projected yield X%” on emerging-market bonds or structured notes at face value, without subtracting currency, credit, and inflation considerations, often ended up with little real gain — or outright losses.
Japan’s Rate Environment (As of May 2026)
At the time of writing (May 2026), the Bank of Japan is gradually normalizing policy while consumer price inflation continues to run around 2%. The 10-year JGB yield is in the mid-1% range. Nominal rates are trending up, but real rates remain low — and in some segments, still negative. The relationship between rates and prices changes constantly, so always check the latest data (e.g., the Statistics Bureau’s CPI release and the BoJ’s Tankan survey) before acting.
A Practical Checklist
- What share of your assets is in cash and deposits?
- Is your deposit interest rate above or below recent inflation?
- Is your mortgage or business loan fixed or variable, and is that choice rational at today’s real rate?
- Are you comparing investment yields on a real, not nominal, basis?
- Can you read central bank announcements through the lens of “how the real rate moves”?
Keeping these five items on a household-budget or business-meeting agenda is useful as a periodic review checklist.
Conclusion
Nominal rates are what you see on the screen; real rates are what your purchasing power actually does. Telling them apart is enough to noticeably raise the quality of your decisions on saving, investing, borrowing, and reading the economy.
You don’t need to memorize complicated formulas. The simple habit of subtracting recent inflation from any rate you see — “Nominal − Inflation ≈ Real” — applied to today’s deposit rate, the loan you’re considering, or that investment product you’ve been eyeing, will already change what you see.
Microfund will continue to track interest rates, inflation, and financing trends, and share insights useful for both household and business decisions. This article is based on information as of May 7, 2026. Rates and prices change daily, so please verify with the latest data before acting.
References
- Irving Fisher, The Theory of Interest: As Determined by Impatience to Spend Income and Opportunity to Invest It, Macmillan, 1930. (The original Fisher equation.)
- N. Gregory Mankiw, Macroeconomics, 11th ed., Worth Publishers, 2022. (Standard treatment of nominal vs. real interest rates.)
- Frederic S. Mishkin, The Economics of Money, Banking, and Financial Markets, 13th ed., Pearson, 2022.
- Olivier Blanchard, Macroeconomics, 8th ed., Pearson, 2020.
- Bank of Japan, Outlook for Economic Activity and Prices (Outlook Report), various issues.
- Bank of Japan, Summary of Opinions at the Monetary Policy Meeting, various issues.
- Statistics Bureau of Japan, Consumer Price Index (CPI), monthly and annual reports.
- Cabinet Office of Japan, Annual Report on the Japanese Economy and Public Finance.
- International Monetary Fund, World Economic Outlook, various issues.
- Bank for International Settlements, BIS Annual Economic Report, various issues.
- Federal Reserve Board, Monetary Policy Report, various issues.