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Investment Calculator

Project the future value of an investment from a starting sum, regular contributions and an assumed return.

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What Investment Calculator does

The future value of an investment is driven by three things: what you start with, what you add, and what rate it grows at over how long. Small differences in any of them compound into large differences in outcome.

This projects the balance and separates what you put in from what growth added.

  • Initial investment, monthly contribution and time horizon
  • Assumed annual return, compounded monthly
  • Split between contributions and growth

How to use Investment Calculator

  1. 1

    Enter your starting amount

    What you are investing today.

  2. 2

    Add regular contributions

    Monthly investing also averages your entry price over time.

  3. 3

    Set the horizon and return

    Test several return assumptions rather than relying on one.

Limits and known behaviour

  • A constant rate of return is assumed. Real returns vary year to year, and the order in which good and bad years arrive changes the result.
  • Inflation is not applied, so figures are nominal.
  • Tax on dividends and gains is not modelled.
  • Platform and fund fees are not deducted, and they compound against the balance in the same way returns compound for it.
  • Nothing here constitutes investment advice, and no investment return is guaranteed.
  • Amounts are calculated and displayed in US dollars using US lending conventions. The arithmetic is currency-independent, so the results hold for another currency if you read the symbol as your own.
  • Figures are estimates for comparison and planning. They are not financial advice, not a quote, and not an offer of credit.

Privacy and data handling

Runs entirely in your browser

  • Every figure you enter stays in this page. What you type about your investments is not transmitted, logged or stored anywhere.
  • There is no account, no saved history and no autosave: reloading the page clears the form.

Site-wide data handling, including analytics and advertising, is described in the privacy policy.

Frequently asked questions

What return should I assume?

There is no correct answer, which is the point of testing a range. Long-run broad equity index returns are often quoted around 7% before inflation, but any particular decade can be far above or below that.

Does this account for inflation?

No. To think in today's money, subtract your inflation assumption from the return: a 7% return with 3% inflation is roughly 4% in real terms.