Percentage price of borrowing or return for lending and saving, whose dollar effect depends on balance, time, and calculation terms.
An interest rate is the percentage price paid for borrowing money or the percentage return associated with lending, saving, or holding an interest-bearing claim over a stated period. The rate does not determine a dollar amount by itself; the applicable balance, time basis, compounding, fees, cash flows, and contract terms also matter.
| Context | Rate applies to | Dollar result |
|---|---|---|
| Deposit | Eligible account balance | Interest credited under account rules |
| Loan | Original or outstanding principal | Interest charged during the period |
| Bond | Face value, market price, or modeled cash flows | Coupon, accrued interest, yield, or price sensitivity |
| Derivative | Contract notional or valuation inputs | Contractual cash flow or present value |
| Valuation | Future cash flows | Present value through discounting |
| Central-bank facility | Eligible reserve, loan, or transaction balance | Administered interest or policy transmission |
The same numerical rate can have different meanings across these contexts. A 5% bond coupon, 5% loan interest rate, 5% deposit APY, and 5% discount rate are not interchangeable.
For constant-principal simple interest:
where:
If USD 25,000 accrues 6% simple interest for one year:
This result assumes the balance and rate remain unchanged and excludes fees and compounding. A loan or deposit with daily balances, payments, withdrawals, tiered rates, or multiple rate periods requires a segmented calculation.
| Label | Main purpose | Main limitation |
|---|---|---|
| Stated interest rate | Applies interest to a balance | May exclude fees and compounding effects |
| Nominal annual rate | Annual quote linked to periodic rates | Does not include within-year compounding |
| Effective Annual Rate | One-year equivalent after compounding | Usually excludes fees unless specifically defined otherwise |
| APR | Annualized borrowing-cost disclosure | Included charges and assumptions depend on applicable rules |
| APY | U.S. deposit yield reflecting rate and compounding | Does not represent an account holder’s after-tax return |
For U.S. deposit disclosures covered by Regulation DD, the interest rate is an annual rate that does not reflect compounding, while APY reflects the interest rate and compounding over a prescribed annual basis.
A nominal rate is stated in money terms. A real rate adjusts for inflation over the same period. The exact one-period relationship is:
where (\pi) is the inflation rate. If a nominal return is 5% and inflation is 2%:
The common approximation gives 3%:
The approximation becomes less accurate as the rates grow. A historical real return also does not guarantee future purchasing-power growth.
A fixed rate does not create a fixed interest amount when the balance changes. A variable rate does not necessarily reset every day. The agreement must define timing, index source, spread, floor, cap, and notice terms.
Rates can reflect:
One policy-rate change therefore does not move every mortgage, deposit, bond yield, or corporate loan by the same amount or at the same speed.
An interest rate can also act as a discount rate. For one future cash flow (CF_t):
Holding the cash flow and risk assumptions constant, a higher discount rate reduces present value. This relationship helps explain why fixed-rate bond prices often fall when market yields rise. Actual asset prices also respond to expected cash flows, credit risk, liquidity, inflation, and changing risk premiums.
This page provides general financial education, not legal, lending, deposit, accounting, tax, investment, or personalized financial advice. Use current product disclosures and market documentation for a specific decision.