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Interest Rate

The percentage charged by a lender for borrowing money, or paid by a bank for depositing money — expressed as an annual percentage of the principal.

Interest Rate

An interest rate is the cost of borrowing money (or the reward for saving it), expressed as a percentage of the principal per year. It is the price of money in financial markets and one of the most important numbers in personal and business finance.

Borrowing vs. Saving

Interest rates work in two directions:

  • Borrowing: You pay interest to the lender for using their money (mortgages, car loans, credit cards)
  • Saving: The bank pays you interest for depositing money they can lend to others (savings accounts, CDs, bonds)

The difference between the rate banks charge borrowers and the rate they pay savers is the spread — the bank's profit margin.

Types of Interest Rates

Simple interest: Calculated only on the original principal.

Interest = Principal × Rate × Time

Compound interest: Calculated on principal plus all accumulated interest. Creates exponential growth (or cost).

A = P × (1 + r/n)^(n×t)

Fixed rate: Stays constant for the loan or investment term. Predictable payments.

Variable (adjustable) rate: Changes periodically based on a benchmark rate (like SOFR or the Prime Rate). Can lower or raise payments unexpectedly.

APR vs. APY

APR (Annual Percentage Rate): The interest rate expressed annually, including fees, without compounding. Used for loans.

APY (Annual Percentage Yield): The effective rate including the effect of compounding. Used for savings accounts and investments.

A savings account with 5% APR compounded monthly has an APY of approximately 5.12%. The APY is always higher than APR for the same nominal rate when compounding is more frequent than annually.

How the Federal Reserve Affects Interest Rates

The Federal Reserve (in the US) sets the federal funds rate — the rate at which banks lend to each other overnight. This benchmark rate influences all other rates in the economy:

  • When the Fed raises rates → mortgage rates, car loans, and credit card rates tend to rise
  • When the Fed cuts rates → borrowing becomes cheaper across the economy

Rates are raised to fight inflation and cut to stimulate economic growth.

Interest Rate and Your Financial Life

| Rate Type | Typical Range (2024) | |-----------|---------------------| | Federal funds rate | 5.25–5.50% | | 30-year mortgage | 6.5–7.5% | | Auto loan (new) | 6.0–8.0% | | Credit card APR | 20–28% | | High-yield savings | 4.5–5.5% | | 10-year Treasury bond | 4.3–4.8% |

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