data / Field guide
What are interest rates?
Understand the price of borrowing, the return to lending, how rates are quoted, and why the Federal Reserve does not set every rate.
An interest rate is a percentage used to calculate the price paid for borrowing money or the return earned for lending or saving it. The dollar result depends on the principal, time period, compounding, fees, and contract terms, so two rates with different definitions may not be directly comparable.
A rate turns time and money into a cost or return
The principal is the amount borrowed or deposited. The interest rate expresses interest relative to that principal for a stated period, often a year. From a borrower's side, interest is a financing cost. From a lender's or saver’s side, it is compensation for providing funds and bearing risks. The same percentage can produce very different dollar amounts when principal or time differs.
For a simple one-year illustration, borrowing $2,000 at 6 percent produces $120 of interest: $2,000 times 0.06. The amount due would be $2,120 if there were no payments, fees, compounding, or other contract terms. Real loans can calculate interest daily, amortize through payments, use a variable rate, or include fees, so the quoted rate alone may not determine total cost.
- Principal: the amount on which interest is calculated.
- Rate: the percentage applied under the contract's time and calculation rules.
- Interest: the resulting dollar cost to a borrower or return to a lender.
Sources: [fed-why-rates-matter]
Compounding and inflation change the interpretation
When interest compounds, later interest can be earned or charged on earlier interest. An illustrative $1,000 deposit earning 4 percent annually becomes $1,040 after one year and $1,081.60 after two: $1,000 times 1.04 squared. Simple interest would produce $1,080 after two years. The difference grows with time and frequency, subject to the account's actual terms.
A nominal rate is stated in current dollars. A real rate adjusts for inflation and better describes purchasing-power change. If a nominal return is 5 percent and inflation is 3 percent, the exact one-year real return is about 1.94 percent: 1.05 divided by 1.03, minus 1. The common subtraction, 5 minus 3 equals 2 percent, is an approximation. Taxes, fees, risk, and the relevant inflation measure can change a person's outcome.
- Illustrative compounding: $1,000 × 1.04² = $1,081.60.
- Illustrative exact real rate: (1.05 / 1.03 - 1) × 100 = about 1.94 percent.
- Compare rates only after aligning period, fixed or variable status, fees, and compounding rules.
There is no single interest rate
Rates differ by borrower risk, collateral, loan length, tax treatment, liquidity, expectations, and market conditions. A secured mortgage, an unsecured credit card balance, a three-month Treasury bill, and a ten-year Treasury note are different promises. Their rates need not move together point for point. Longer-term rates reflect expectations about future short-term rates and the broader economy, not just today's policy setting.
A percentage point is not the same as a percent change. A rate moving from 4 percent to 5 percent rises by one percentage point, or 100 basis points. Relative to 4 percent, that is a 25 percent increase in the rate itself. Stating which comparison is intended prevents a common error, but neither description alone tells you the change in a particular payment.
- One percentage point equals 100 basis points.
- Fixed rates remain set under contract terms; variable rates can reset using a stated benchmark and rules.
- Maturity and credit risk are part of the product, not noise around one universal rate.
Sources: [fed-policy-workings] [fed-prime-rate]
What the Federal Reserve sets, and what it influences
The Federal Open Market Committee sets a target range for the federal funds rate, the overnight rate at which depository institutions lend reserve balances to one another. The Federal Reserve explains that changes in this target are transmitted quickly to many short-term market rates and floating-rate loans. The effects on longer-term borrowing also depend on expectations and financial conditions.
The Fed does not directly set every mortgage, savings, credit-card, or prime rate. Banks set the prime rate, often partly with reference to the federal funds target. Lenders add product costs and risk judgments, while savers' rates also reflect competition and funding needs. Higher rates tend to restrain some borrowing and spending; lower rates tend to encourage them, but these are tendencies with lags, not guarantees for every household or business.
- Policy rate: an overnight interbank target used to influence broader financial conditions.
- Market rate: a rate formed through trading, expectations, and risk in a particular market.
- Retail rate: a lender's or bank's offered rate under specific product and customer terms.
Sources: [fed-policy-workings] [fed-why-rates-matter] [fed-prime-rate]
Primary sources
- Why do interest rates matter?Board of Governors of the Federal Reserve System · accessed 2026-10-19
- Monetary Policy: What Are Its Goals? How Does It Work?Board of Governors of the Federal Reserve System · accessed 2026-10-19
- What is the prime rate, and does the Federal Reserve set the prime rate?Board of Governors of the Federal Reserve System · accessed 2026-10-19
Prepared with AI assistance and reviewed against the linked primary sources. This is public financial education, not personal financial or investment advice.
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