A jar at home keeps your money in one place. A bank is like a giant jar that lots of people share. It keeps everyone's money safe, remembers how much belongs to each person, and gives it back when you ask.
Your jar in this app works the same way. The jar diary is like the list a real bank keeps: every coin in and every coin out.
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What is interest?
πͺ β¨
Interest is extra money the bank adds to your jar, just for keeping your money there.
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Why does the bank pay you?
The bank doesn't just leave your money in a drawer. It lends money to other people, like a family buying a house or a baker buying a new oven.
π§ You save
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π¦ Bank lends
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π§βπ³ Baker pays back a bit extra
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β¨ You get a share
People who borrow pay the bank back a little more than they borrowed. The bank shares part of that extra with savers like you. That share is your interest. The bank keeps the rest to pay its workers and keep the lights on.
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Interest on interest
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Here's the clever part. When the bank pays you interest, it goes into your jar. Next time, the bank pays interest on your money and on the interest it already gave you. This is called compounding.
It works like a snowball rolling down a hill: the bigger it gets, the faster it grows.
Year
In the jar at the start
Interest on your money
Interest on interest
In the jar at the end
Look at the gold column. That money was earned by old interest. It starts tiny and keeps getting bigger every year.
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The race
Two jars start with the same money. One only earns interest on the money you put in. The other also earns interest on its interest. Slide to see who wins.
Only on your money
Interest on interest
Check what you learned
Grown-up corner
This app pays interest on set days and rounds to the cent. Real banks usually count interest every day and pay it monthly. They show the yearly rate with compounding included, called APY in the US and AER in the UK.
"The bank lends out your savings" is the classroom version. In reality, banks create new money when they make loans, and deposits are one of the ways they fund that lending.
Real savings are protected by deposit insurance up to a limit, for example $250,000 per depositor per bank in the US (FDIC) and β¬100,000 in the EU.
A good next talk: if prices rise faster than the interest rate (inflation), the money in the jar buys less over time, even while the number goes up.
Tip: a generous parent rate (like 10%) makes compounding visible in weeks instead of years. Real savings rates are much lower, which is worth discussing.