In plain words: Interest calculated on the initial principal, which also includes all of the accumulated interest from previous periods.
Compound interest is the engine behind long-term investing. Because each period's gains are added back to the base, future returns are earned on a growing pile rather than the original amount alone. Over many years this snowball effect can turn modest, regular contributions into a much larger sum.
How does compounding actually work?
Imagine an amount that grows by a steady rate each year. In year one you earn a return on your contribution; in year two you earn a return on that contribution plus last year's gain, and so on. The longer the asset is held, the more the curve bends upward, which is why time is the most powerful ingredient in how compound interest works.
Why does time matter more than amount?
Starting earlier often beats contributing more later, because each extra year gives the snowball more room to roll. A diversified mix of broad asset classes such as global equities and bonds can let returns reinvest and compound, though real returns vary and are never guaranteed.
Key takeaways
- Compounding earns returns on both your principal and prior gains.
- Time in the market is usually more decisive than the exact amount invested.
- Reinvesting returns lets the growth curve accelerate over the long run.