How Does Interest Work? Interest Rates for Beginners | EarnIn

November 13, 2023

How Does Interest Work? Interest Rates for Beginners

As the old saying goes, there’s no such thing as a free lunch — or a free loan.

That’s why borrowers must understand interest rates. But savers and investors should also understand interest if they want to maximize their results.

So, how does interest work? And what is an interest rate? Put simply, interest is a fee one must pay to borrow money. It is often calculated as an interest rate, a percentage of the amount loaned that accumulates over time.

Interest is a fundamental facet of personal finance. Whether you realize it or not, you’ve most likely interacted with interest before, either by paying interest on a line of credit or collecting interest from a savings account.

How do interest rates work?

Several factors determine interest rates, including central bank policies (such as the U.S. Federal Reserve), monetary supply, inflation, economic conditions, and market demand.

Interest rates determine your return over a given timeframe when you're investing or saving money. For instance, if you put money in a savings account, the bank pays you interest for the privilege of using your money, and your total balance grows.

On the other hand, when you're borrowing money, interest rates determine your total cost of borrowing. If you take out a loan, you'll need to repay the borrowed amount and the accrued interest. Lower rates mean lower costs. Higher rates mean higher costs.

Financial institutions calculate interest in several ways, so you should pay close attention to the terms of your contract.

Some interest rates are fixed, meaning they’ll remain constant for the duration of a loan or investment. Others change over time — known as variable rates. You should also note whether interest is compounding, or “compound interest,” meaning you earn or pay interest on the principal amount as well as any accrued interest. Interest that only applies to the principal amount is called “simple interest.”

Interest rates are a vital part of financial planning, debt management, and investment decisions. When you're paying for a car or buying a home, interest rates will affect the total cost. And when you’re saving money, interest rates will affect how fast your savings grow.

Pros and cons of interest rates

Interest isn’t just a financial math problem; it serves an invaluable function in influencing economic activity and power. Advantages of interest rates include:

1. Promoting saving: High interest rates on savings accounts and investments incentivize individuals to save money and build wealth over time.

2. Controlling inflation: Central banks adjust interest rates to control inflation. Raising rates usually helps temper inflation, whereas lowering rates often stimulates consumer demand.

3. Bolstering spending via borrowing: Lower interest rates can make borrowing more affordable, encouraging businesses to invest in projects and encouraging people to make purchases.

Despite the advantages, sometimes interest rates have negative impacts on consumers. Some of those are:

1. Making borrowing unaffordable: Higher interest rates can lead to higher borrowing costs, making it more challenging for individuals and businesses to access credit.

2. Eroding savings: When interest rates are low, the return on savings accounts and investments may not keep up with inflation.

3. Market volatility: Rapid changes in interest rates can cause uncertainty and market volatility, affecting stock prices and overall economic stability.

Types of interest

Interest rates come in various forms, each with its own effects. Whether you’re borrowing, investing, or saving, consider the type of interest rate being applied.

Simple interest

Simple interest is calculated only on the principal (the initial sum that’s borrowed or invested). It doesn't consider the interest earned or paid. Simple interest is commonly used in straightforward loan agreements or short-term investments.

For example, if you borrow $100 with 5% simple interest, the loan will accrue a flat $5 in interest each year, even as the amount you owe increases annually.

Compound interest

Compound interest factors in the initial principal as well as the interest that accumulates over time. Compound interest causes investments to grow faster over time. On the other hand, it can lead to higher borrowing costs and runaway debt.

To illustrate compound interest, consider the previous example. If the interest compounded, you would owe $105 on your $100 loan after the first year. However, the 5% interest would be calculated on the entire amount owed in the second year, meaning your additional interest would be $5.25.

Methods for calculating interest

Financial institutions represent interest in various ways that provide different information about how the amount owed will grow over time.

Nominal interest rate

A nominal interest rate doesn’t factor in inflation or the frequency of compounding periods. It gives a straightforward but less useful picture of how a debt or investment grows.

Real interest rate

A real interest rate adjusts the nominal rate for inflation, providing a more accurate representation of the actual purchasing power of money.

For example, if the nominal interest rate on your savings account is 2%, but the rate of inflation is 5%, your money actually loses 3% of its purchasing power each year.


The effective annual rate (EAR), also known as annual percentage yield (APY), is used for savings and investments. It represents the total earnings from an investment or savings account over a year, factoring in how often interest compounds. It provides a more accurate representation of the true annual cost or return of an investment or loan.


The annual percentage rate (APR) represents the overall cost of borrowing, including interest and fees. It's used for loans and credit cards, helping borrowers understand the total cost of a loan. Note that it does not account for compounding interest.

How to avoid interest charges

To minimize interest charges, try these techniques:

1. Pay credit card balances in full: Clear credit card balances by the due date to avoid accruing interest.

2. Choose low-interest loans: Opt for loans bearing lower interest rates to reduce the overall cost of borrowing.

3. Save wisely: Search for high-interest savings accounts to maximize returns over time.

4. Maintain a good credit score: A higher credit score often qualifies you for lower interest rates on loans and credit cards, reducing your borrowing costs.

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Please note, the material collected in this post is for informational purposes only and is not intended to be relied upon as or construed as advice regarding any specific circumstances. Nor is it an endorsement of any organization or Services.

EarnIn is a financial technology company, not a bank. Bank products are issued by Evolve Bank & Trust, Member FDIC. The EarnIn Card is issued pursuant to a license from Visa USA Inc.

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