€10,000 invested for 20 years and never touched
Invest €10,000 once, leave it completely alone, and at a 5% annual return it becomes €27,126 after 20 years. You never add another cent, yet €17,126 of that total is growth the money earned on its own through compound interest.
The scenario
The setup is deliberately simple. You put in €10,000 today. You make no further deposits, no withdrawals, and no adjustments for two decades. The only thing doing any work is time and a steady annual rate of return. This isolates a single question: how much difference does the rate make when the time horizon is fixed at 20 years?
The result at three rates
| Annual rate | Value after 20 years | Growth on your €10,000 |
|---|---|---|
| 3% | €18,208 | €8,208 |
| 5% | €27,126 | €17,126 |
| 7% | €40,387 | €30,387 |
What it shows
Nothing changes in this scenario except the rate. You don’t invest more, you don’t check the balance, you don’t do anything at all. Patience is the only input you supply. Everything else is arithmetic.
The rate sensitivity across the rows is stark. Moving from 3% to 5% doesn’t just add two percentage points of growth — it more than doubles the euro amount of growth, from €8,208 to €17,126. Moving from 5% to 7% takes the total to €40,387. Small differences in rate compound into large differences in outcome, precisely because compound interest builds each year’s gains on top of every previous year’s gains, not just on the original €10,000.
At 5%, the €10,000 has more than doubled by year 20, reaching €27,126. This lines up with the Rule of 72, a rough mental shortcut for estimating how long money takes to double: divide 72 by the annual rate. At 5%, that’s 72 ÷ 5, or roughly 14 years to double. With six more years left to run after that doubling point, it’s consistent with the balance climbing well past double the original €10,000 by year 20.
Try your own numbers
The figures here assume a single lump sum, no additions, and a constant rate held steady for the full 20 years. Real investments don’t move in a straight line — returns vary year to year, and fees or taxes can take a share of the growth. The exercise is still useful as a baseline: it shows what time and a steady rate can do on their own, before you complicate the picture with contributions, withdrawals, or a variable rate. Put your own starting amount, timeframe and rate through the compound interest calculator to see where they land.