Compound growth explained with a simple example

Compound growth explained

Compound growth means the returns you earn start earning returns of their own. Over a few years the effect is small, but over decades it can become the biggest part of your money.

Growth on top of growth

Say you invest €10,000 and it grows 5% in a year. You gain €500 and now have €10,500. In the second year, 5% is worked out on €10,500, not €10,000, so you gain €525 and end with €11,025.

That extra €25 is growth on last year's growth. It looks tiny at first. The point is that it keeps getting bigger every year the money stays invested.

A worked example over 30 years

Here is the same €10,000 with an assumed return of 5% a year, with growth added once a year and nothing taken out. The 5% is only an assumption for the arithmetic; real returns go up and down and are not known in advance.

After 10 years: €10,000 × 1.05^10 ≈ €16,289
After 20 years: €10,000 × 1.05^20 ≈ €26,533
After 30 years: €10,000 × 1.05^30 ≈ €43,219

Compare it with simple growth

With simple growth, you would earn 5% on the original €10,000 only, which is €500 a year. After 30 years that is €10,000 + 30 × €500 = €25,000.

Compound growth gives about €43,219 in the same example, so roughly €18,219 more. None of that difference came from extra money you put in. It came only from leaving the gains invested.

Notice too that the second 10 years added more (about €10,244) than the first 10 years (about €6,289). Time is the main ingredient, which is why starting earlier, even with a small amount, can matter more than starting later with a bigger one.

What slows compounding down

Compounding works on whatever is left after everything that comes out. Four things reduce it:

Fees: a yearly cost is taken out before the growth compounds. See why fees matter.
Withdrawals: money you take out stops compounding.
Losses: a fall of 20% needs a rise of 25% just to get back to where you were, because 80 × 1.25 = 100.
Inflation: rising prices mean each euro buys less later. See what inflation does to your money.

It works the other way with debt

Compounding is not only for savings. Interest on debt that you do not pay off compounds in the same way, which is why high-interest debt can grow fast. If you are deciding between the two, see pay off debt or invest.

Key takeaways

Compound growth means your returns earn returns of their own.
Time does most of the work: later years add more than early ones.
Fees, withdrawals, losses and inflation all reduce what compounds.

Try it

The calculator is prefilled with €10,000, no monthly additions, an assumed 5% a year and 30 years. Change the years to see how much time matters. Its result can differ slightly from the figures here if it compounds more often than once a year.

Run the €10,000 example

Quick check

3 questions. Pick an answer to see why it's right or wrong.

You have €10,500 after one year and earn 5% in the second year. How much do you gain in year two?
Show the answer
€525 – In the second year, 5% is worked out on €10,500, not €10,000, so you gain €525 and end with €11,025.
In the 30-year example, where did the extra money from compounding come from?
Show the answer
From leaving the gains invested – It came only from leaving the gains invested.
After a 20% fall, what rise do you need to get back to where you started?
Show the answer
25% – Losses: a fall of 20% needs a rise of 25% just to get back to where you were, because 80 × 1.25 = 100.

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Last reviewed 25 Oct 2026

Education, not advice. I'm not a financial adviser and I don't know your situation. These tools show the maths behind common rules of thumb; check important decisions with a qualified professional. Full disclaimer.