Albert Einstein once said—or at least is credited with saying—that compound interest is “the eighth wonder of the world. He who understands it, earns it… he who doesn’t, pays it.”
Although the quote is probably not his, it contains two undeniable truths:
- Compound interest is one of the most powerful forces for growing your wealth in the long term.
- And most importantly: it’s better to have it working for you than against you.
What is compound interest?
Compound interest allows you to earn returns not only on your initial capital but also on the interest already accumulated. In other words, your earnings generate additional earnings.
A visual way to think of it is as a “snowball effect.” This effect amplifies over time, making it your best ally.
We’ve covered this topic extensively on our blog, and you can explore it in more depth from different perspectives:
- What is compound interest, and how does it work?
- Compound interest and its multiplying effect
- How to save through compound interest
We’ve even looked at it from a more educational angle:
And also from its negative side:
Let’s look at a practical example: if you invest €1,000 at an annual return of 5.5% for 30 years without making any additional contributions, you could end up with around €5,000.
The impact of recurring contributions and time
But if you also contribute €150 per month, after 30 years the result exceeds €142,000—having contributed only €55,000 yourself. That means more than €85,000 comes purely from compounded growth.
When it comes to compound interest, time is everything.
Put another way, the key is to start as early as possible. Starting your investments at age 30 with regular contributions has a much greater effect than starting 10 or 20 years later—even if you contribute more each month. At inbestMe, we make this easy: you can start with a small amount from €1,000 (or €250 for pension plans) with an automated strategy tailored to your profile and goals.
Let’s continue with the example (see graph above): we saw that by starting with €1,000 at age 30 and contributing €150 per month, by age 60, with an interest rate of 5.5%, you’d have €142,539. If instead, you started investing at age 40 or 50, and thus only had an investment horizon of 20 or 10 years, you’d need to contribute €292 per month (if starting at 40) or €760 per month (if starting at 50) to reach the same amount by age 60.
This shows the exceptional impact of starting earlier: the more time your money has to grow, the less you need to contribute each month to reach the same final goal.
Good and simple financial habits multiply the effect
Understanding compound interest is just the first step.
The second is to put it into practice through consistent habits: save part of your income as soon as you receive it (pay yourself first or pay your future self), review your contributions regularly, and increase them as your income grows.
Automating the process with recurring contributions—as inbestMe allows—makes it a sustainable and effective habit.
All you have to do is click the “Recurring Contribution” button (second button from the right) and follow the steps.
Additionally, staying invested is crucial. Market volatility can be scary, but history shows that long-term investors tend to be the most successful. The longer your time horizon, the better.
As Warren Buffett said: “your time horizon is your best asset,” because it magnifies the effect of compound interest.
The rate of return is very important
In the previous examples, we used an annual return (APY) of 5.5%. The following graph shows how the return rate has a significant impact:
- If the annual return dropped to 4.5%, the final capital would be much lower (€118,500).
- On the other hand, if the return rose to 6.5%, the result would be much higher (€172,195).
That’s why it’s so important to ensure that your investments are not only well-diversified, but also aligned with your time horizon and profile to maximize outcomes.
Investing in index funds, like those we use at inbestMe, allows you to capture global market returns with efficient management and minimal fees. For example, while traditional savings deposits have offered average returns of around 1% in recent decades, our diversified index fund portfolios have expected returns between 3% and 7% depending on risk profile. Although past returns are not a guarantee of future performance, as of the end of 2024, historical returns generally exceeded those expectations.
In the graph above, the difference between investing at 1% and 5.5% over 30 years—with an initial €1,000 and monthly contributions of €150—is clear: €64,587 vs. €142,539.
Long-term investing in index portfolios not only gives you access to potential returns but also protects your money from inflation—the silent enemy of savings.
Automate the process with the Goal Forecaster
You don’t need to build complex spreadsheets to run the simulations we’ve discussed.
A few months ago, we launched the Goal Forecaster for that very purpose.
The Goal Forecaster is an excellent option to help you go fully automatic and simulate and track the progress of your goals.
To activate it, simply click “Set Goal” within each account (remember, you can have different accounts for different goals). You just need to define the time frame and target amount, and you’ll get an indication of the additional or recurring contribution you need to program.
Aim to reach a success probability of 65% or higher as soon as possible. To do that, make periodic contributions—ideally automated—and then let go. Reviewing your strategy once a year and making small adjustments (only if you’re below that 65%) will be more than enough.
Just a few months after its launch, 15% of our clients have already activated this tool. While this initial figure is encouraging, we strongly believe its potential is much greater, and we aim for the vast majority of our users to benefit from it.
Don’t wait any longer—using it significantly increases your chances of reaching your goals and puts you in autopilot mode.
This will help shield you from emotions and market volatility, and allow you to focus on the more important parts of your life.
Compound interest and recurring investment: a winning formula
Compound interest won’t make you rich overnight, but it can help you build significant wealth over time. The earlier you start, the better—even with small amounts.
At inbestMe, we provide all the tools to help you make the most of compound interest: automation, diversification, low fees, and an efficient investment philosophy based on indexation.
Your financial future isn’t built through grand gestures, but rather through small, smart decisions repeated over time.
Start early, invest consistently, and let time do the rest.
Compound interest and recurring investment are a winning formula.
