Compound Interest Calculator

See how your money grows with compound interest over time

Real-time | 100% client-side
Investment Details

$0

Future Value

$0

Total Invested

$0

Total Interest

0 yrs

Doubling Time

Growth Over Time

Principal + Contributions Interest Earned

Year-by-Year Breakdown

Year Deposits Interest Balance

Key Insights

  • Interest as % of total 0%
  • Effective annual rate 0%
  • Rule of 72 estimate 0 yrs

Quick Scenarios

Formula

A = P(1 + r/n)nt
  • A = Future value
  • P = Principal (initial investment)
  • r = Annual interest rate (decimal)
  • n = Compounds per year
  • t = Time in years

100% Private

All calculations happen locally in your browser. Your financial data is never sent to any server or stored anywhere.

How Compound Interest Works

Understanding the most powerful force in personal finance

Compound interest is often called the "eighth wonder of the world" — and for good reason. Unlike simple interest, which only earns returns on your original deposit, compound interest earns returns on both the principal and previously accumulated interest. This creates an exponential growth curve that accelerates over time.

For example, $10,000 invested at 7% annual interest compounded monthly will grow to approximately $19,672 in 10 years — nearly double — without adding a single extra dollar. Add a modest $200 monthly contribution, and that figure jumps to $53,829. The key insight is that time in the market matters more than the amount invested.

Exponential Growth

Compound interest grows slowly at first, then accelerates dramatically. The longer you stay invested, the more powerful the compounding effect becomes.

Time Is Key

Starting early is more important than investing larger amounts later. A 25-year-old investing $200/month will have more at 65 than a 35-year-old investing $400/month.

Frequency Matters

More frequent compounding means slightly higher returns. Daily compounding earns more than monthly, which earns more than annually, though the differences are small.

Compound Interest vs. Simple Interest

See how much more you earn with compound interest

Feature Simple Interest Compound Interest
Interest on Principal only Principal + accumulated interest
Growth pattern Linear Exponential
$10K at 7% for 10 years $17,000 $19,672
$10K at 7% for 20 years $24,000 $38,697
$10K at 7% for 30 years $31,000 $76,123
Best for Short-term, simple loans Savings, investments, retirement

Frequently Asked Questions

Common questions about compound interest and investing

Compound interest is interest earned on both the initial deposit (principal) and the interest that has already been added to it. This creates a snowball effect where your money grows faster over time, because each period's interest is calculated on a larger and larger base amount.
The formula is A = P(1 + r/n)nt, where 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 monthly contributions, each payment is compounded separately from its deposit date.
Simple interest is calculated only on the original principal: Interest = P × r × t. Compound interest is calculated on the principal plus all previously earned interest. Over long periods, compound interest produces dramatically higher returns. For example, $10,000 at 7% for 30 years yields $31,000 with simple interest but $76,123 with compound interest.
More frequent compounding produces higher returns, but the differences are small. Monthly compounding is standard for savings accounts and CDs. Daily compounding is offered by some high-yield accounts. The difference between monthly and daily on $10,000 at 5% over 10 years is only about $30.
The Rule of 72 is a quick mental math shortcut: divide 72 by the annual interest rate to estimate how many years it takes to double your money. At 6%, it takes about 12 years. At 8%, about 9 years. At 12%, about 6 years. This rule is most accurate for rates between 4% and 12%.
This calculator shows nominal returns before taxes and inflation. In reality, investment gains may be subject to capital gains tax, and inflation reduces purchasing power. For a rough real return estimate, subtract the inflation rate (typically 2–3%) from your interest rate.