How Savings Grow With Interest
Compound interest is the way savings grow when a bank pays interest not only on the money you first put in, but also on the interest it has already added. If you save $100 at 5% a year, the bank adds $5 in the first year. In the second year the 5% is worked out on $105, so you earn $5.25 — a little more than before. Each year the base gets bigger, so each year's interest gets bigger too.
That contrasts with simple interest, where the bank always pays 5% of the original $100, giving a flat $5 every year. Over one or two years the gap looks tiny. Over ten years, compounding pulls clearly ahead, and over twenty or thirty years the difference is large.
The idea rests on three things a young saver can grasp: percent means "out of every 100"; next year's total = money you have now + interest on that money; and time matters more than the amount you start with, because the growth builds on itself. The same maths explains why borrowing money — on a loan or credit card — can get expensive if it is not paid off quickly.
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Money that grows🐷 ✨ 🏦 Money That Grows While You Sleep Imagine you put $100 in a bank. You do nothing at all… and next year you have more than $100. That extra money is called interest. Let's find out how it works — and why waiting makes it grow faster and faster. Today 1 year 5 years 10 years Money is a bit like a plant. Give it time, and it grows on its own.
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Why the bank pays youWhy does a bank give you money? 🤔 When you keep your money in a bank, the bank borrows it for a while. It lends your money to other people — and it says thank you by paying you a little extra. That thank-you money is interest. Tap the jar that grows 👇 Two children each have $100. Where will the money grow? 🫙 Aisha's jar at home Money in a jar stays exactly the same. $100 today, $100 in ten years. Nothing wrong with it — it just doesn't grow! 🏦 Ben's bank account Yes! The bank uses Ben's money and pays him interest for letting it. Ben's $100 slowly turns into more than $100. Tap a jar to see wh
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One year of interestInterest for one year Banks say things like “5% a year”. The little % sign means “out of every 100”. 5% means: for every $100 you save, the bank adds $5 after one year. $100 saved → tap the button to wait one year ⏳ Wait one year Reset You have $100. No interest yet. Each gold coin = $10. The green coins that appear are your interest.
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Interest on your interestThe clever part: interest on interest 🌱 Here is the trick that makes savings grow faster and faster. In year 2, the bank does not give you interest on $100 any more. It gives you interest on $105 — your money plus last year's interest! 🔁 The Year Machine Start: $100. Interest rate: 5% each year. Press the button to run a year. Year0 Interest added$0 Total$100.00 ▶ Run a year Start over Press “Run a year” and watch the green tops get taller. Notice: the interest is $5.00, then $5.25, then $5.51… It gets bigger every single year, even though you never add a cent yourself. That is called compound
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Build the ruleBuild the money rule 🧩 Every year the bank does the same two steps. Drag (or tap) the pieces into the right order. Next year's total = ? + ? money you have now 5% of the money you have now 5% of $100, always Drag a card into a box — or tap a card, then tap a box. The tricky trap: “5% of $100, always” is what simple interest does. Compound interest is smarter — it always takes 5% of your new, bigger total.
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The 10-year raceThe 10-year race 🏁 Two friends both save $100 at 5%. Sara gets simple interest (always $5 a year). Kai gets compound interest. Slide to see the years fly by! Years: 0 🙋♀️ Sarasimple $100 🙋♂️ Kaicompound $100 At year 0 they are exactly the same. Your turn 🎯 Slide all the way to year 10 first. Then answer: after 10 years, how much more does Kai have than Sara (to the nearest dollar)? Exactly the same — $0 more About $2 more About $13 more About $100 more Move the slider to year 10 and compare the two numbers.
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Time is the superpowerTime is the real superpower ⏰ Compound interest starts slowly, then speeds up. The longer you leave money alone, the bigger the jump. $100 at 5%, left completely alone: After…You haveInterest earned 1 year$105$5 5 years$128$28 10 years$163$63 20 years$265$165 From year 10 to year 20, it earns $102 — more than in the first ten years put together! Choose wisely 🧠 Two boxes. Tap the one you think is worth more after 15 years. 🌰 $50 saved for 15 years Correct! At 5%, $50 grows to about $104. Fifteen years of compounding beat a bigger start with almost no time. 💵 $90 saved for 2 years Close, but no
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You did it!🏆 Well done, super saver! You now understand something many grown-ups find tricky. Interest = extra money the bank adds for keeping your savings there. 5% a year means $5 added for every $100 saved. Compound interest = you earn interest on your savings and on the interest you already earned. That's why the yearly interest grows: $5.00 → $5.25 → $5.51 → … Simple interest always pays the same amount; compound keeps speeding up. The two magic ingredients are time and patience. Start early, leave it alone. Try this at home 🏠 Ask a grown-up what interest rate their savings account pays. Then work o
Frequently asked questions
- Why does the bank pay me money just for keeping my savings there?
- A bank does not leave your money sitting in a vault — it lends it out to other people and businesses who pay to borrow it. Interest is the bank's thank-you for letting it use your money, and it is why your balance grows even when you do nothing.
- What does 5% interest a year actually mean in dollars?
- Per cent means "out of every 100", so 5% means $5 is added for every $100 you have saved. On $100 that is $5 after one year; on $200 it would be $10; on $40 it would be $2.
- What is the difference between simple interest and compound interest?
- Simple interest is always worked out on the original amount, so it pays the same dollars every year. Compound interest is worked out on your current total, which includes past interest, so the amount added grows a little more each year.
- At what age can a child in Singapore understand compound interest?
- The core idea — add a percentage, then add it again on the bigger number — is within reach of most children by Primary 4 to Primary 6, once percentages and simple multiplication are familiar. Younger children can still follow it using round numbers like $100 at 5%.
- Does compound interest work against you as well?
- Yes. Loans and credit cards charge interest on the amount still owed, including interest already added, so an unpaid debt grows in the same accelerating way. That is why paying off borrowed money early costs far less than leaving it.
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