Interest and Compound Growth
Interest is the price of borrowing or the reward for saving.
About this topic
Interest is the price of borrowing money or the reward for saving it, expressed as a percentage rate. Simple interest is calculated only on the original principal: I = Prt. Compound interest is paid on the principal and previously earned interest: A = P(1 + r/n)^(nt), where P is principal, r the annual rate, n the compounding periods per year and t the years.
Compounding makes growth accelerate over time, which is why starting early matters so much. It also works against borrowers who carry debt. The rule of 72 gives a quick estimate: divide 72 by the interest rate to find the years needed to double money.
Example: 1,000 dollars at 5 percent simple interest earns 50 dollars every year, so 500 dollars in 10 years, ending with 1,500. With annual compounding it becomes 1,000 times 1.05 to the power of 10, about 1,629 dollars. After 40 years, simple interest gives 3,000 while compounding gives about 7,040. At 6 percent, money doubles in about 12 years. Savings accounts, bonds, student loans and mortgages all use these formulas.
Misconceptions: a higher number of compounding periods helps only a little compared with a higher rate or longer time. Also compare loans using the APR, not just the nominal rate. Tip: time is the most powerful ingredient.
Key ideas
- Simple vs compound interest
- Rule of 72
- Start early
Quick check
Use cases: where Interest and Compound Growth helps
- Homework: review the key idea behind Interest and Compound Growth before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Interest and Compound Growth without notes.
- Visual learning: play with the interactive lab to see how Interest and Compound Growth changes when you adjust its inputs.
- Teaching a friend: explain Interest and Compound Growth in your own words, then compare your version with the key ideas.
Economics explains prices, jobs, budgets and government policy in daily life.
Frequently asked questions
What is Interest and Compound Growth?
Interest is the price of borrowing or the reward for saving.
What will I learn in Interest and Compound Growth?
Simple vs compound interest. Rule of 72. Start early.
Is Interest and Compound Growth part of Economics & Money?
Yes. It is one of 30 Economics & Money topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Interest and Compound Growth lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Interest and Compound Growth?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.