A savings account or certificate of deposit may advertise an attractive annual percentage yield, but that number does not show whether your purchasing power is growing. To evaluate a deposit, compare its nominal return with inflation, then account for taxes, fees, and withdrawal rules.
Quick Answer
A deposit produces a positive real return only when its after-tax growth is greater than inflation over the same period. A hypothetical 4.00% APY with 3.5% inflation earns about 0.48% before tax, but the real return could become negative after taxes.
What Is a Nominal Interest Rate?
A nominal interest rate is a rate stated without adjusting for inflation. It shows how quickly the dollar balance of an account may increase.
For U.S. savings accounts and CDs, consumers will often see an annual percentage yield, or APY. APY includes the effect of compounding and provides a standardized way to compare deposit accounts. CFPB Regulation DD establishes the rules for calculating and disclosing APY.
The nominal return tells you how many dollars you may earn. It does not tell you how much those dollars will buy after prices change.
What Is a Real Interest Rate?
A real interest rate adjusts the nominal return for inflation. It measures the change in purchasing power rather than only the change in the account balance.
| Measure | What It Shows | Inflation Included? |
|---|---|---|
| Nominal return | Growth in the dollar balance | No |
| Real return | Growth in purchasing power | Yes |
A balance can increase while its real value decreases. This happens when inflation rises faster than the account’s return.
How to Calculate a Real Interest Rate
Federal Reserve educational materials use this simple approximation:
Real interest rate ≈ nominal interest rate − inflation rate
For example, a 4.00% nominal return minus 3.50% inflation equals an estimated real return of 0.50%. This subtraction method is useful for quick comparisons.
The Exact Real-Return Formula
For a more accurate result, use the following calculation:
Exact real return = (1 + nominal return) ÷ (1 + inflation rate) − 1
Enter percentages as decimals. A 4.00% return becomes 0.04, and 3.50% inflation becomes 0.035.
(1.04 ÷ 1.035) − 1 = approximately 0.48%
The exact result is slightly lower than the simple 0.50% estimate.
Example: $10,000 in Savings at 4.00% APY
This is a hypothetical one-year example, not a current bank offer. It uses the 3.5% annual CPI inflation rate reported for June 2026.
| Item | Example Amount |
|---|---|
| Starting balance | $10,000 |
| APY | 4.00% |
| Gross interest | $400 |
| Ending balance before tax | $10,400 |
| Inflation rate | 3.50% |
| Exact real return before tax | Approximately 0.48% |
The U.S. Bureau of Labor Statistics reported that the Consumer Price Index for All Urban Consumers increased 3.5% from June 2025 through June 2026. The release was published on July 14, 2026. This is a backward-looking figure, not a forecast for a new 12-month deposit.
After adjusting for 3.5% inflation, the $10,400 ending balance would have purchasing power equal to about $10,048 in beginning-of-period dollars. The nominal gain is $400, but the real purchasing-power gain is only about $48 before tax.
What Happens After Federal Income Tax?
Assume, only for this example, that the saver’s federal marginal tax rate is 22%.
- Federal tax on $400 of interest: $88
- After-tax interest: $312
- After-tax ending balance: $10,312
- Exact after-tax real return: approximately -0.37%
- Purchasing-power change: approximately -$37
The balance still increases by $312 after the example federal tax. However, inflation rises faster than the after-tax balance, producing a small loss of purchasing power.
Why Taxes Can Change the Result
The IRS states that most interest received or credited to an account is taxable income, although certain types of interest may be tax-exempt. Bank interest is generally taxed as ordinary income for federal purposes. Actual tax liability depends on taxable income, filing status, deductions, and applicable state rules.
A simple after-tax estimate is:
Estimated after-tax return = APY × (1 − marginal tax rate)
This is an educational estimate, not an official tax calculation. State income taxes, account fees, and individual tax circumstances can further affect the result.
Which Inflation Rate Should You Use?
The CPI measures price changes for a broad basket of goods and services purchased by urban consumers. It is a useful national benchmark, but it may not match an individual household’s spending pattern.
A household spending more on rent, health care, food, child care, or energy may experience a different personal inflation rate. A past CPI rate also cannot predict inflation during a new savings-account or CD term.
Use expected inflation for a forward-looking estimate. After the account period ends, use the actual inflation change over the matching period to evaluate the final real return.
What to Check Before Opening an Account
- Compare APY rather than only the stated interest rate.
- Confirm whether the APY is fixed, variable, promotional, or balance-based.
- Review minimum-balance requirements and monthly fees.
- Estimate federal and state taxes on the interest.
- Compare the return and inflation rate over the same period.
- For a CD, check its maturity date and automatic-renewal terms.
- Review any early-withdrawal penalty before depositing funds.
FDIC guidance explains that CDs generally require money to remain deposited for a specified term and may impose an early-withdrawal penalty. The account disclosure should provide the APY, interest rate, balance requirements, fees, and other important conditions.
The Bottom Line
A higher savings rate does not automatically mean your money is gaining purchasing power. Start with the APY, estimate the after-tax return, and compare it with inflation over the same period.
A positive real return means the savings may buy more. A negative real return means the balance grows while purchasing power falls. Review the official account disclosure and consider taxes, fees, liquidity, and inflation together before opening an account.
Official information checked July 29, 2026: U.S. Bureau of Labor Statistics Consumer Price Index, IRS Topic No. 403, CFPB Regulation DD, Federal Reserve Education, and FDIC consumer guidance.