Compound Interest Calculator

Calculate how your savings grow with compound interest over time. See the power of compounding with yearly, monthly, or daily contributions. This tool processes all data locally in your browser. No information is ever sent to any server. Completely free, no registration required.

How to Use the Compound Interest Calculator

1. Enter your input values above
2. Results update automatically
3. Copy or download the output

What is a Compound Interest Calculator?

A Compound Interest Calculator shows how your money grows over time when you earn interest on both your original investment AND the accumulated interest from previous periods. Albert Einstein reportedly called compound interest 'the eighth wonder of the world' and 'the most powerful force in the universe.' Unlike simple interest (earned only on the principal), compound interest creates exponential growth — a small amount invested regularly can grow into substantial wealth over decades. This calculator helps you visualize that growth and plan for retirement, education savings, or any long-term financial goal.

How Does It Work?

The calculator uses the compound interest formula: A = P(1 + r/n)^(nt), where A is the future value, P is the principal, r is the annual interest rate (as a decimal), n is the number of times interest compounds per year, and t is the number of years. For regular contributions, the formula extends to include the future value of an annuity. The more frequently interest compounds (daily vs. annually), the faster your money grows.

Formula

Future Value = P(1 + r/n)^(nt) + PMT × [(1 + r/n)^(nt) − 1] / (r/n)\n\nWhere:\nP = Initial Principal\nr = Annual Interest Rate (decimal)\nn = Compounds per Year (12=monthly, 365=daily)\nt = Years\nPMT = Periodic Contribution

Who Uses This Tool?

• Retirement planning — see how 401(k) contributions grow over 30+ years
• College savings — calculate how much to save monthly for your child's education
• Investment goal setting — determine how long until you reach a savings target
• Comparing investment options — see the impact of different interest rates
• Teaching financial literacy — visualize the power of starting early

Pro Tips

• Start early — a 25-year-old investing $200/month at 7% will have ~$525,000 by age 65. Starting at 35 yields only ~$244,000
• Increase contributions by just 1% each year — it's barely noticeable but dramatically increases your final balance
• Reinvest dividends — they're a form of compound growth too
• Higher compounding frequency = faster growth. Monthly beats annual, daily beats monthly

Frequently Asked Questions about Compound Interest Calculator

What's the difference between APY and APR?

APY (Annual Percentage Yield) includes the effect of compounding and shows your actual annual return. APR (Annual Percentage Rate) is the simple rate without compounding. For example, 5% APR compounded monthly = 5.12% APY.

How much should I save for retirement?

A common guideline is to save 15% of your pre-tax income for retirement (including employer match). Use our Retirement Calculator for a personalized estimate based on your age, income, and goals.

Does compounding really make that much difference?

Yes. A $10,000 investment at 7% for 30 years grows to $76,123 with compounding — but only $31,000 with simple interest. That's $45,123 extra from compounding alone. Now imagine the difference with monthly contributions!

Free online Compound Interest Calculator — no signup, 100% client-side processing. All data stays in your browser.