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Compound Interest Calculator

Calculate compound interest with monthly contributions, multiple compounding frequencies, and inflation adjustment. See a year-by-year growth chart, milestone markers, and your real purchasing power over time.

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Disclaimer: This calculator provides estimates for educational purposes only. It does not constitute financial advice. Actual investment returns vary based on market conditions, fees, and other factors. Consult a qualified financial advisor for investment decisions.

Quick Facts

Rule of 72 (at 7%)~10.3 years to double
Einstein on compound interest"8th wonder of the world"
S&P 500 avg return~10% nominal
US avg inflation~3% historically

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How to Use This Calculator

  1. Enter your initial investment amount.
  2. Set the annual interest rate and compounding frequency.
  3. Add monthly contributions if applicable.
  4. Optionally enable inflation adjustment to see real purchasing power.
  5. View the live chart showing your balance growth over time.

The Formula

A = P(1 + r/n)^(nt) + PMT × [((1 + r/n)^(nt) - 1) / (r/n)]. Where: P = principal, r = annual rate, n = compounding frequency, t = years, PMT = periodic contribution. Continuous: A = Pe^(rt).

Frequently Asked Questions

Compound interest is interest earned on both the original principal and on previously accumulated interest. Unlike simple interest (which only earns on the principal), compound interest accelerates growth over time — the longer your money compounds, the faster it grows.