Compound Interest Calculator

Compound interest represents interest earned not only on the initial principal deposit, but also on the accumulated interest generated during prior periods. This feedback loop transforms arithmetic growth into exponential expansion over multi-decade horizons.

The core formula A = P(1 + r/n)^(nt) demonstrates that the duration of investment (t) exerts far greater leverage on final portfolio value than the initial principal (P). Because time resides in the exponent, compounding accelerates dramatically in the later years of an investment term, creating what economists refer to as the "hockey stick" accumulation curve.

The frequency with which interest is credited (n) affects the effective annual yield (EAY). For an account yielding an 8% stated nominal rate, compounding annually yields exactly 8.00%. Compounding monthly increases the effective annual rate to 8.30%, while compounding daily increases it to 8.33%.

While the mathematical difference between monthly and daily compounding is modest for retail accounts, compounding frequency becomes significant when paired with regular monthly contributions, as earlier deposits begin accruing periodic interest immediately.

When modeling long-term wealth targets (such as retirement or college funds), nominal growth figures must be adjusted for the erosive effects of inflation. If a portfolio achieves an 8% nominal annual return while inflation averages 3%, the true purchasing-power growth (the real return) is approximately 5% per year.

Similarly, taxable brokerage accounts subject interest distributions and realized capital gains to annual tax drag, reducing the compounding efficiency. Utilizing tax-advantaged accounts (such as 401(k)s, IRAs, ISAs, or superannuation) shields the compounding cycle from tax friction.