Beginner guide

What Is Compound Interest?

Compound interest is interest earned on both your starting balance and the interest already added along the way. That is why time matters so much: growth can start to build on top of growth.

Simple definition

If you earn interest and leave it invested, the next period can earn interest on a slightly larger balance. Repeating that process over years is what creates compounding.

Quick example

Invest $1,000 at 5% per year. After year one, you have $1,050. After year two, you earn 5% on $1,050, not just on the original $1,000. That is the compounding effect.

What matters most

TimeThe longer money stays invested, the more periods it has to compound.

Rate of returnHigher returns can speed up growth, but they often come with higher risk.

Regular contributionsConsistent deposits can be more powerful than chasing tiny formula differences.

Compound interest vs simple interest

Simple interest only pays on the original amount. Compound interest pays on the original amount plus previously earned interest. Over long periods, compound interest usually pulls away.

Where people misunderstand it

They overestimate the impact of compounding frequency and underestimate the power of time.
They ignore inflation, fees, or taxes when looking at a final balance.
They use a formula meant for lump sums when they are really making recurring deposits.

A simple picture of compound interest

Compound interest is interest earned on both your original money and the interest it has already earned. Put $1,000 in at 8% and after one year you have $1,080. The next year you earn 8% on $1,080, not just the original $1,000 — and that head start keeps building. After 20 years the $1,000 becomes $4,661.

$1,000 at 8%

$1,000 at 8% compound interest: small at first, then visibly accelerating — the snowball effect.