Compound Interest

Compound interest is the process where your money earns interest on both your original investment and the interest it has already accumulated, causing your investment to grow faster over time.

What is compound interest?

Compound interest is when you earn interest not only on the money you first invested (the principal) but also on the interest that has already been added. Over time, you are earning “interest on interest,” which makes your money grow faster.

Think of it like a snowball rolling down a hill: it starts small, but as it rolls, it picks up more snow and becomes larger. The longer it rolls, the bigger it gets. In the same way, the longer your money is invested, the more it grows through compound interest.

How does compound interest work

The growth depends on three main factors:

The amount you invest – More money at the start can lead to faster growth.
The interest rate – A higher rate means more growth over time.
Time – The longer you leave your money invested, the more powerful compounding becomes.

Even small amounts can grow significantly if given enough time.

Formula:

Compound Interest = [P × (1 + i)^n] − P

Compound Interest = P × [(1 + i)^n − 1]

Where:

P = principal (the starting amount)
i = annual interest rate (as a decimal, e.g., 0.05 for 5%)
n = number of compounding periods

Example:
Suppose you invest €5,000 at 6% annual interest, compounded yearly, for 4 years. Using the formula: Compound Interest=5,000×[(1+0.06)4−1]=5,000×[1.2625−1]=5,000×0.2625=1,312.50\text{Compound Interest} = 5,000 \times [(1 + 0.06)^4 – 1] = 5,000 \times [1.2625 – 1] = 5,000 \times 0.2625 = 1,312.50Compound Interest=5,000×[(1+0.06)4−1]=5,000×[1.2625−1]=5,000×0.2625=1,312.50

The interest earned over 4 years is €1,312.50, making the total amount €6,312.50.

The snowball effect

Compound interest works like a snowball rolling down a hill: it starts small but grows bigger as it rolls and picks up more snow. In investing, your principal earns interest, and then that interest earns interest in the following periods — this is the “snowball effect.”

Dividends accelerate the snowball

Dividends can further boost compounding. By reinvesting dividend payments, you are adding more “snow” to your snowball. Each reinvested dividend earns returns just like your original investment, making your portfolio grow faster over time.

For example, if you own dividend-paying stocks or ETFs, each dividend increases your share count. Those additional shares then earn dividends themselves, creating a cycle of growth that makes your portfolio grow faster over time.

Final thoughts

Compound interest is one of the most powerful tools in long-term investing. Time and consistency are your greatest allies. Even modest investments can grow substantially if left to compound over years or decades. Reinvesting dividends amplifies this growth, making compounding a cornerstone of building wealth.