Public Knowledge Library / Money & Saving

05 4 min read

How compound interest works

Compound interest means your money earns returns on the original amount and on previous earnings too. Over time, that changes growth from a line into a curve.

A fast estimate

Rule of 72

72 / interest rate = years to double

It is a rough shortcut, but it makes the idea of compounding much easier to picture.

6%About 12 years to double
9%About 8 years to double
12%About 6 years to double

Why it feels slow at first

Early on, most of the growth still comes from your original balance.

Later, the interest earned on past interest becomes a larger share of the total. That is when compounding starts to feel dramatic.

Big takeaway

Time does the heavy lifting.

Starting earlier often matters more than making a perfect move later, because extra years give your gains more chances to earn gains of their own.

Three practical reminders

01

Start now

A smaller amount with more years can outperform a bigger amount that starts much later.

02

Reinvest the earnings

Compounding is strongest when the returns stay in the account and keep working.

03

Be patient

The snowball is quiet before it is impressive. Most of the power shows up late, not early.

Keep exploring

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