Compound Interest Calculator

See how your money grows over time with compound interest and regular contributions.

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$
$
%
yr
Final balance
$0
after 20 years
Initial
$0
Contributed
$0
Interest earned
$0
Principal Contributions Interest
Year Balance Interest Total contrib.
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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 only earns on the principal), compound interest earns on its own earnings — creating exponential growth over time. Albert Einstein reportedly called it "the eighth wonder of the world".

The compounding frequency matters: daily compounding earns slightly more than monthly, which earns more than annually, because interest is reinvested more frequently. For a long-term investment, the difference between monthly and daily compounding is small — but the difference between 7% and 8% annual return over 30 years is enormous. Regular contributions often have a bigger impact than the compounding frequency.

How to Use

  1. Enter your initial investment (can be zero).
  2. Enter a monthly contribution (can be zero for lump-sum only).
  3. Set the annual interest rate and investment period.
  4. Choose how often interest compounds.
  5. Results and the year-by-year table update instantly.

Frequently Asked Questions

The US stock market (S&P 500) has returned approximately 10% annually on average before inflation, or about 7% after inflation. A globally diversified index fund is often used at 6–8% for long-term projections. Savings accounts and bonds typically yield 2–5%. For retirement planning, many financial planners use 6–7% as a conservative real-return estimate.

No — this calculator shows nominal growth before taxes and inflation. To approximate real (inflation-adjusted) returns, subtract the inflation rate from your interest rate (e.g. use 4.5% instead of 7% if inflation is 2.5%). Tax treatment depends on your account type (tax-advantaged accounts like 401k or ISA grow tax-free or tax-deferred).

No. All calculations happen entirely in your browser. Nothing is sent to any server.
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