Introduction
Imagine a small snowball rolling down a hill. At first it is tiny, and it grows slowly. As it rolls, it picks up more snow. Soon it is bigger, so it picks up even more snow with each turn. By the end of the hill, it is huge. Money can grow in the same way. That is the simple idea behind compound interest.
Interest is extra money paid for using money. When you save money, the bank pays you interest. When you borrow money, you pay interest to the bank. Compound interest is interest that is paid on your starting money and also on the interest you have already earned. Your money earns money, and then that new money earns money too. That is why people call it a snowball.
What It Is
Compound interest is interest on interest. It is different from simple interest, and the difference matters a lot over time. Simple interest is interest paid only on your starting money. It never changes, because it always uses the same starting number. Compound interest uses a bigger number each time, because the interest you earned is added to your money.
Your starting money has a simple name. People call it the principal, but you can just think of it as your starting money. If you put $1,000 in a savings account, your starting money is $1,000. In the first year, you earn interest on $1,000. In the second year, you earn interest on $1,000 plus the interest from the first year. That is the whole trick. Your money grows a little faster each year, because the base keeps getting bigger.
How It Works
Compound interest works in small steps, one step at a time. At the end of each year, the bank adds interest to your account. Your balance goes up by a small amount. In the next year, the bank works out interest on the new, bigger balance. So you earn a little more interest than you did the year before. This keeps going, year after year, and the growth gets faster over time.
The key is to leave the interest in the account. If you take the interest out and spend it, your balance stays the same. Then the next year looks just like the last year, and that is simple interest, not compound interest. But if you leave the interest in, it joins your starting money. Then it starts to earn interest too. That is why time matters so much, and why starting early helps even with a small amount.
How often the interest is added also matters a little. Some accounts add interest once a year, and some add it once a month. Adding it more often means the interest starts earning interest sooner. The difference is small at first, but it grows over many years. The biggest factors are still the same three things. They are how much you start with, the interest rate, and how long you leave the money alone.
An Example With Numbers
Let us use a clear example with easy numbers. This is an example only, not a promise of a real rate. Imagine you put $1,000 in an account that pays 5% interest per year. The interest is added once a year, and you do not add or take out any money. In the first year, you earn 5% of $1,000, which is $50. Your balance is now $1,050. That first year looks the same for simple interest and compound interest.
In the second year, the two types split apart. With simple interest, you earn $50 again, because simple interest always uses the starting $1,000. Your balance is $1,100. With compound interest, you earn 5% of $1,050, which is $52.50. Your balance is $1,102.50. The difference is only $2.50, but it is real. In the third year, compound interest earns 5% of $1,102.50, which is $55.13, and the balance is $1,157.63. The gap keeps growing.
After 10 years, the gap is easy to see. With simple interest, you earn $50 each year for 10 years, which is $500 in total. Your final balance is $1,500. With compound interest, your final balance is $1,628.89. You earned $628.89 in interest, which is $128.89 more than simple interest. The formula for this is simple to read. You take your starting money, times 1.05, and you do that 10 times, once for each year. After 20 years at the same 5%, the same $1,000 would grow to $2,653.30, and that shows how time makes the snowball bigger.
Common Mistakes
One common mistake is to wait for a big amount before you start saving. People think $1,000 is too small to matter, so they wait. But compound interest rewards time more than size. A small amount left alone for a long time can grow more than a big amount left alone for a short time. You can start with a small amount in a TFSA, which is a Tax-Free Savings Account. You can read a simple guide in What Is a TFSA? Simple Guide for Canadian Students. The key is to start, and then to leave the money alone.
A second mistake is to take the interest out too soon. If you spend the interest each year, you break the snowball. Your balance stops growing faster, and you go back to simple interest. That is fine if you need the money, but it is not the best way to grow savings. A better habit is to leave the interest in the account and let it work for you. If you want to compare a TFSA with an RRSP, which is a Registered Retirement Savings Plan, read What Is RRSP vs TFSA in Canada?.
A third mistake is to forget that compound interest also works against you on debt. When you borrow money, interest can build up on the interest you already owe. That is why credit card debt can grow so fast if you pay only the minimum amount. The same snowball that helps your savings can hurt you when you owe money. So use compound interest as a friend for saving, and be careful with it when you borrow.
Final Thoughts
Compound interest is simple to understand, but it is powerful over time. Your starting money earns interest, and that interest earns interest too. The growth starts slow, and then it gets faster. You do not need a big amount to start, and you do not need a hard plan. You need time, patience, and the habit of leaving the money alone. Start small, start early, and let the snowball roll.
Quick Questions
What is compound interest in simple words? Compound interest is interest earned on your starting money plus the interest you have already earned. Your money earns money, and then that new money earns money too.
How much is $1,000 at 5% after 10 years with compound interest? With interest added once a year, $1,000 at 5% grows to $1,628.89 after 10 years. With simple interest at the same rate, it would grow to only $1,500.
Is compound interest better than simple interest? Yes, for saving, compound interest gives you more money over time because it pays interest on past interest too. For borrowing, it can cost you more, so it is best to pay debt down fast.
Disclaimer: This article is for educational and informational purposes only and does not constitute financial advice.
Sources: Investopedia definition via BridgeView Advisors — https://www.bridgeviewadvisors.com/compound-interest-2/ ; Simple vs Compound Interest, worked example — https://www.toolnimbly.com/blog/simple-vs-compound-interest-examples ; Compound Interest Formula Explained Simply — https://www.bankdepositguide.com/articles/compound-interest-formula-explained ; How compound interest works, whiteboard explainer — https://www.rekkaai.com/blog/compound-interest-explained