Compound Interest Calculator 2026

It shows what your money becomes if you reinvest your gains instead of cashing them out. Enter your starting amount, monthly top-ups, and expected return. The result is a projection — real markets don't move in straight lines, and your actual returns won't match a flat rate assumption.

Compound interest means you earn returns on your previous returns, not just your original deposit. Invest 100,000 at 10%. Year 1: you earn 10,000. Year 2: you earn 11,000 (10% on 110,000). Year 3: 12,100. The gap between simple and compound gets wider every year — that's why starting early beats investing larger amounts later.

Divide 72 by your annual return rate to estimate how many years it takes to double your money. At 8%: 72/8 = 9 years. At 12%: 6 years. At 6%: 12 years. Works best for rates between 6-12%. It's a quick mental check — no calculator needed.

Yes — credit card debt at a high APR compounds just like investments, except it's compounding against you. A balance carried with only minimum payments can take decades to clear and cost far more than the original amount in interest. If you're earning 10% on investments while paying 25%+ on debt, you're losing money overall every year. Clear high-interest debt before investing.

No — standard compound interest calculators show nominal returns before taxes. Real return is roughly the nominal rate minus the inflation rate (10% nominal with 6% inflation is about 4% real), and taxes on interest or gains reduce your effective return further, depending on your country's tax rules. Use the after-inflation, after-tax number for retirement or long-term planning, not the headline figure.