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Index Fund Calculator

Project index fund investment growth with lump sum and regular contributions. See long-term compound returns.

Last reviewed 15 August 2026

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Calculator inputs

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When to use this calculator

  • Before choosing between saving, investing or changing a contribution.
  • When you want to compare cautious, base and optimistic return assumptions.
  • When you need a projection before making a longer-term decision.
  • When you want to see whether starting earlier or contributing more changes the outcome more.

A realistic US planning example

Use these sample inputs as a quick scenario test, then change one variable at a time to compare outcomes.

A realistic US planning example
InputValue
Initial Investment ($)$15,000
Monthly Contribution ($)$250 per month
Expected Annual Return (%)8
Years10 years

After entering these figures, review portfolio value, total invested and growth together rather than in isolation. Then rerun the tool with one input adjusted.

How to read your results

Portfolio Value

The figure produced by this output for the inputs you entered. Change one variable at a time if you want to see what drives it.

Total Invested

The headline outcome of this calculation. It is most useful when read alongside the supporting metrics rather than in isolation.

Growth

The figure produced by this output for the inputs you entered. Change one variable at a time if you want to see what drives it.

Common mistakes

  • !Using an assumption that is not supported by a current local quote, bill, statement or official source.
  • !Treating a generic estimate as a lender, provider, payroll or tax authority decision.
  • !Mixing monthly and annual inputs without converting them consistently.
  • !Testing only one scenario instead of checking how a cautious assumption changes the result.

What to do next

  • Run a second scenario with a cautious assumption so you can see the downside clearly.
  • Compare the result with the related calculators below before making a decision.
  • Check current local rules, eligibility and provider terms before applying or committing money.
  • Keep a record of the assumptions so you can update the estimate when a quote, bill or pay figure changes.

Frequently asked

Global equity index funds have historically returned around 7–10% per year over long periods (20+ years), though past performance does not guarantee future results.

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