Albert Einstein reportedly called compound interest the eighth wonder of the world. He said that those who understand it earn it, and those who do not pay it. While that quote might be an exaggeration, the math behind compound interest is indeed powerful.
To understand compound interest, you first need to understand simple interest. Simple interest is when you earn interest only on the money you originally deposited. Compound interest, on the other hand, is when you earn interest on your original deposit *plus* the interest you have already accumulated.
The Compounding Growth Table
To visualize this, look at how a single $10,000 deposit grows over 30 years at an annual interest rate of 6%, compounded annually, compared to simple interest:
| Year | Simple Interest Balance | Compound Interest Balance | Compounding Advantage |
|---|---|---|---|
| Year 0 | $10,000 | $10,000 | $0 |
| Year 5 | $13,000 | $13,382 | +$382 |
| Year 10 | $16,000 | $17,908 | +$1,908 |
| Year 20 | $22,000 | $32,071 | +$10,071 |
| Year 30 | $28,000 | $57,434 | +$29,434 |
By Year 30, the compounding account is worth more than double the simple interest account, showing how compounding accelerates growth over long periods.
The Power of Time
The most critical ingredient in compound interest is time. The longer your money sits and grows, the faster the compounding effect accelerates.
This is why starting to save early is so vital. A person who starts saving a small amount in their twenties will often end up with much more money by retirement than someone who starts saving double that amount in their forties.
If you want to see the numbers for your own situation, try using our compound interest calculator to project how your monthly contributions will grow over ten, twenty, or thirty years.