In the world of personal finance, compound interest stands out as a game-changer—a force that can transform modest savings into substantial wealth, especially if you start investing early. Across Europe, from London to Lisbon, this timeless principle is the key to building a secure financial future. Whether you’re a young professional in Berlin or a mid-career saver in Madrid, understanding how compound interest works and acting on it now can set you up for life. In this in-depth guide, we’ll explore what compound interest is, why starting early gives Europeans a massive edge, and how you can leverage it in 2025 to grow your wealth in euros.