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Compound Interest Calculator

Project investment growth with contributions and compound interest.

Your data stays in your browser and is never uploaded to a server.

Estimates only; actual returns may vary.

Projection methodology

Separate what you contribute from what the assumed return produces

A compound-interest projection is a scenario, not a promise. The result combines the initial principal, periodic contributions and returns generated under one constant annual-rate and compounding assumption.

Worked example: monthly contributions for ten years

Start with $10,000, add $250 at the end of each month, assume 7% annually and compound monthly for 10 years.

Inputs and process

  1. 1Initial principal: $10,000
  2. 2Monthly contributions: $250 × 120 = $30,000
  3. 3Total amount contributed: $40,000
  4. 4Nominal annual rate: 7%, compounded monthly

Result

The calculator projects about $63,367.82: $40,000 contributed and $23,367.82 of modeled interest.

About 36.9% of the projected ending balance comes from modeled interest. That split changes with contribution timing, rate, fees and the path of actual returns.

How to read the projection

“Future value” is the modeled ending balance. “Contributions” is money supplied by the user, while “interest earned” is the difference between that balance and total supplied capital.

The comparison without contributions isolates growth of the initial principal. It is not a recommendation to stop contributing; it shows how much of the scenario depends on ongoing deposits.

Real use cases

Savings scenarios

Compare a conservative, central and optimistic rate without treating any one path as guaranteed.

Contribution planning

See how recurring deposits change the ending balance relative to the initial principal alone.

Fee awareness

Reduce the assumed net return to explore how ongoing costs can affect a long horizon.

Sources and review

Last editorial review:

How to calculate compound interest

  1. 1

    Enter principal, contributions and rate.

  2. 2

    Choose contribution and compounding frequencies.

  3. 3

    Calculate and review growth, table and CSV.

Key features

Precise calculations

Typed financial formulas run locally in your browser.

Currency formatting

Present results in USD, EUR or CRC without exchange rates.

Clear breakdown

Tables, summaries and CSV exports show every result.

Frequently asked questions

Are these results guaranteed?

No. They are estimates based on the values entered.

Are exchange rates applied?

No. Currency only controls symbols and formatting.

Is my financial data uploaded?

No. Every calculation runs in your browser.

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