Compound Interest Calculator — Free Savings & Investment Tool

Compound Interest Calculator

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Free Compound Interest Calculator

Calculate how your savings and investments grow over time with our free compound interest calculator. Whether you're planning for retirement, saving for a goal, or comparing investment scenarios, this tool provides detailed projections with interactive charts.

How to Use

  1. Enter your initial investment amount
  2. Set the annual interest rate and compounding frequency
  3. Add regular contributions (monthly, weekly, etc.)
  4. Optionally adjust for inflation and taxes
  5. Click Calculate to see your projected growth

Features

  • Regular contributions — Model monthly, weekly, or annual deposits
  • Inflation adjustment — See your returns in real purchasing power
  • Tax impact — Factor in tax rates on interest income
  • Interactive chart — Visualize growth of principal vs. interest
  • Year-by-year breakdown — Detailed table of balances over time
  • Export results — Download as CSV or JSON
  • Privacy-first — 100% client-side, your data never leaves your browser

The Power of Compound Interest

Albert Einstein reportedly called compound interest the "eighth wonder of the world." The key insight is that your interest earns interest, creating exponential growth over time. Starting early and contributing regularly are the two most powerful factors — even small amounts grow dramatically over decades.

Frequently Asked Questions

What is compound interest?
Compound interest is interest calculated on both the initial principal and the accumulated interest from previous periods. Unlike simple interest, which is only calculated on the principal, compound interest grows exponentially over time — making it one of the most powerful concepts in finance.
How is compound interest calculated?
The formula is A = P(1 + r/n)^(nt), where P is the principal, r is the annual interest rate, n is the number of times interest is compounded per year, and t is the number of years. Our calculator also accounts for regular contributions and inflation adjustments.
What is the difference between APR and APY?
APR (Annual Percentage Rate) is the stated interest rate without accounting for compounding. APY (Annual Percentage Yield) includes the effect of compounding and represents the actual annual return. APY is always equal to or higher than APR.
How often should interest be compounded?
More frequent compounding yields slightly higher returns. Daily compounding earns more than monthly, which earns more than annually. However, the difference between daily and monthly compounding is usually minimal for most savings accounts.
How does inflation affect my savings?
Inflation reduces the purchasing power of your money over time. Our calculator lets you toggle inflation adjustment to see your returns in "real" (inflation-adjusted) terms. A 7% return with 3% inflation gives approximately 4% real growth.
Is my financial data stored?
No. All calculations happen entirely in your browser using JavaScript. Your financial data never leaves your device — there are no server requests, no cookies, and no tracking.
What is the Rule of 72?
The Rule of 72 is a quick way to estimate how long it takes to double your money. Divide 72 by your annual interest rate. For example, at 8% interest, your money doubles in approximately 72 ÷ 8 = 9 years.

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