How compounding actually works
Compound interest means the interest you earn starts earning interest of its own. In the first year that effect is small — almost invisible. The point of this calculator is to show what it does over ten or twenty years, where the "growth earned" figure can rival or exceed everything you contributed. Nothing about that requires luck or skill; it requires time and not interrupting it.
The three levers, ranked
- Time. Doubling the years far more than doubles the growth, because the later years compound on a much bigger base. Starting early with a small amount usually beats starting late with a large one.
- The contribution. The monthly amount is the lever you control most directly. Try changing it above and watch the future value move.
- The rate. It matters — but it is the lever people obsess over while neglecting the other two, and chasing an unrealistically high rate is how people end up in schemes. If a promised rate is far above what banks and government securities pay in your country, read our guide to checking a provider is licensed before anything else.
Real rates, inflation and tax
The result here is in tomorrow's money, not today's purchasing power. If inflation in your country runs at, say, a similar level to your interest rate, the real growth is close to zero even though the number gets bigger. Two practical consequences:
- Compare any savings rate against your country's inflation rate to judge whether money is genuinely growing.
- Interest is taxed in many markets, often withheld before it reaches you — so the rate to type in is the after-tax rate if you want a realistic answer. Your country's Rateweb site covers the local treatment.
This tool runs entirely in your browser — nothing you type is sent to us or stored. Results are estimates for education, not financial advice; real products carry fees and taxes this generic tool cannot know. More tools: see the full list.