Interest rates in plain English
An interest rate is a price for the use of money. A borrower pays interest to a lender; a bank may pay interest to a depositor. Rates are normally expressed annually, but the contract determines how interest accrues, compounds, and is applied.
A quoted 7% loan rate does not mean the borrower simply pays 7% of original principal once. Interest may accrue daily or monthly on the outstanding balance, and the repayment term changes total dollars paid.
The interest rate is also not necessarily the APR. APR is a standardized broader measure that can incorporate certain finance charges. Compare rate, APR, fees, payment, term, and total cost together.
Simple-interest calculation
For a basic simple-interest example:
Interest = principal × annual rate × time in years
Borrowing $10,000 at 6% simple annual interest for one year produces $600 of interest. Real installment loans usually make payments during the year, so principal declines and interest is calculated on the remaining balance.
Daily simple interest can use:
Daily interest = outstanding principal × annual rate ÷ day-count basis
The basis may be 365, 360, or another contract convention. Payment timing therefore matters.
Nominal rate, effective rate, and yield
A nominal annual rate may not reflect intra-year compounding. If interest compounds monthly, the effective annual rate is higher than the nominal rate because interest earns or incurs interest.
Effective annual rate = (1 + periodic rate)^periods − 1
For deposit products, annual percentage yield (APY) standardizes the effect of compounding. For loans, APR follows product-specific disclosure rules and may include certain fees.
Do not compare a deposit APY directly with a loan APR as though they measure identical cash flows.
Interest rate versus APR
The CFPB explains that a loan's interest rate is the price paid to borrow principal, while APR combines the rate with certain additional charges. On a mortgage, APR can reflect points, broker fees, and other costs.
APR is useful for comparing similar offers, but it has limits:
- it assumes a particular holding and payment pattern;
- adjustable-rate APR does not show the maximum future rate;
- excluded fees still affect cash cost;
- different product types use different rules; and
- a loan repaid early can have a different realized cost.
Review the Loan Estimate's interest rate on page 1 and APR in the Comparisons section, along with five-year cost and Total Interest Percentage when applicable.
Fixed interest rates
A fixed rate does not change for the contractual fixed period. On a fully amortizing fixed-rate mortgage, scheduled principal and interest generally remain constant, although taxes, homeowners insurance, mortgage insurance, and escrow can change the total payment.
Fixed rates provide payment predictability but can begin above an adjustable introductory rate. Refinancing later is not guaranteed and creates new underwriting and closing costs.
Some loans use a fixed rate but variable payment because of nonstandard amortization, fees, or escrow. “Fixed” describes the rate, not every dollar due.
Variable and adjustable rates
A variable rate changes according to the contract. It may equal an index plus a margin:
New rate = reference index + lender margin, subject to caps and floors.
An adjustable-rate mortgage can have an initial fixed period, adjustment frequency, initial cap, periodic cap, lifetime cap, and floor. A 5/1 ARM commonly fixes the initial rate for five years and then adjusts annually, but the note controls.
Evaluate the maximum possible payment, not only the introductory rate. Index changes can lower or raise future payments, and a floor can limit decreases.
What determines a borrower's rate
Lenders consider market conditions and borrower-specific risk. Factors can include:
- product and loan term;
- credit history and score;
- debt-to-income ratio;
- down payment or loan-to-value;
- collateral and occupancy;
- loan amount and purpose;
- rate lock period;
- points and lender credits; and
- lender pricing and competition.
Rates advertised publicly may assume excellent credit, a particular down payment, points, occupancy, property, and short lock. Request personalized disclosures.
Benchmarks and the Federal Reserve
The Federal Reserve sets a target range for the federal funds rate, which influences short-term financing conditions. It does not directly set each mortgage, credit-card, auto, or savings rate.
Mortgage rates reflect expectations for inflation, longer-term Treasury and mortgage-backed-security markets, credit risk, servicing, capital, and demand. A Fed policy change and a mortgage-rate move can differ in timing or direction because markets anticipate future policy.
Prime rate and SOFR are examples of benchmarks used in some variable-rate products. Identify the exact index, publication source, observation date, margin, caps, and fallback language.
Points and lender credits
Mortgage discount points are upfront fees paid in exchange for a lower rate. One point generally equals 1% of loan amount, but the rate reduction per point varies.
Estimate break-even:
Break-even months = additional upfront cost ÷ monthly payment savings
This ignores time value, tax effects, balance differences, and an early sale or refinance, but it is a useful screen.
A lender credit moves in the other direction: the lender offsets some closing costs in exchange for a higher rate. Compare options for the expected holding period, not just cash due today.
Rate locks
A mortgage rate lock holds specified pricing for a defined period, subject to conditions. Confirm the rate, points or credits, expiration date, lock fee, extension policy, and what happens if closing is delayed.
A floating rate can change before closing. A lock may not protect pricing if loan amount, credit, property, occupancy, or other material facts change.
Get the lock confirmation in writing and track the closing schedule. Do not assume a verbal quote is locked.
Interest rate and amortization
For the same principal and term, a higher rate increases payment and total interest. For the same rate and principal, a longer term reduces the monthly payment but generally increases total interest.
Early amortizing payments allocate more to interest because principal is larger. Paying additional principal can reduce future interest on loans that accrue interest on the outstanding balance, subject to posting rules and prepayment terms.
Use an amortization schedule, but reconcile it with the contract's actual accrual method.
Credit cards
Credit-card APRs can vary by transaction type: purchases, balance transfers, cash advances, or penalties. A card can use a variable APR tied to an index and calculate periodic interest from an average daily balance.
A grace period may allow purchases to avoid interest when the statement balance is paid in full by the due date, but cash advances often begin accruing immediately. Carrying a promotional balance can interact with grace-period rules.
Read the Schumer box and card agreement for APRs, fees, minimum interest, compounding, and allocation of payments above the minimum.
Deposit interest rates
For savings and certificates of deposit, compare APY rather than nominal rate because APY incorporates compounding. Check minimum balance, tiering, fees, withdrawal limits, CD term, and early-withdrawal penalties.
A high rate can be temporary or apply only to a balance tier. Deposit insurance eligibility depends on institution, ownership category, and amount—not the advertised rate.
Real return is roughly nominal return minus inflation and taxes, though exact calculation is multiplicative.
Comparing rate offers correctly
Collect quotes close together because market rates move. Give lenders the same loan amount, term, property, down payment, lock period, and point preference.
Then compare:
- interest rate and whether it is fixed or adjustable;
- APR;
- points, credits, and lender fees;
- principal-and-interest and total payment;
- cash to close;
- costs over the expected holding period; and
- prepayment, balloon, or negative-amortization features.
The lowest rate is not automatically the cheapest offer if it requires expensive points. The lowest payment may simply extend debt longer.
An interest rate is a critical input, but not a complete decision. Translate the percentage into dollars, timing, risk, and the period you realistically expect to keep the account.