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Investment Calculator

Estimate how a starting amount and regular monthly or annual contributions could grow at an expected return, with contribution timing, yearly increases and inflation.

  • Free, no sign-up
  • Runs in your browser
  • Finance
Contributions
Contribute at the
Optional. Raises the contribution once a year.
Return and time
Optional. Shows the balance in today's money.

How to use the investment calculator

Enter a starting amount, a contribution amount and how often you contribute (monthly or annual). Choose whether each contribution goes in at the start or the end of the period, then enter the expected annual return and the number of years. Two fields are optional:

  • Annual contribution increase raises your contribution once a year, for example 3% to keep pace with a growing salary.
  • Inflation converts the end balance into today's money, so you can see its real purchasing power.

Press Calculate to see the end balance, total contributions, total growth and, if you entered inflation, the inflation-adjusted balance. The table below shows each year's contributions, growth and ending balance.

How it differs from the savings and compound interest calculators

The savings and compound interest calculators start from a quoted interest rate with a compounding frequency, such as 5% compounded monthly, and always add deposits at the end of the period. This calculator is built for investments:

  • The expected return is treated as an effective annual return, the way investment returns are usually reported. A 7% return means the starting amount grows by exactly 7% each year.
  • You choose the contribution timing. Money invested at the start of a period earns that period's return as well.
  • You can see the real return after inflation, and you can test negative returns down to -50% a year.

The method

The annual return R is turned into an equivalent period rate i = (1 + R)^(1/m) − 1, where m is 12 for monthly and 1 for annual contributions. Each period the balance grows by i. An end-of-period contribution is added after the growth; a start-of-period contribution is added before it. The inflation-adjusted balance is the end balance divided by (1 + inflation)^years.

Worked example

You start with 10,000 and add 500 at the end of each month for 10 years at a 7% expected return. The starting amount grows to 10,000 × 1.07^10 = 19,671.51 and the contributions to 85,525.87, so the end balance is 105,197.38. You put in 70,000 in total, and 35,197.38 is growth.

If you invest the 500 at the start of each month instead, the end balance rises to 105,680.95. With 3% inflation, that is worth about 78,636.56 in today's money.

Good to know

  • Real investments do not earn a steady return. Markets rise and fall, so treat the results as estimates, not financial advice or a promise of future performance.
  • Fees, taxes and trading costs are not included and can reduce your return noticeably over long periods.
  • Use a few different return rates to see a cautious, a middle and an optimistic outcome.

Frequently asked questions

What return should I enter?

Use a long-term average that fits your mix of investments, and try a lower and a higher figure as well. The calculator applies the same return every year, while real markets vary from year to year, so the result is an estimate rather than a forecast.

Does contributing at the start of the period make a big difference?

It adds one period of growth to every contribution. In the example of 500 a month for 10 years at 7%, investing at the start of each month instead of the end adds about 480 to the end balance.

What does the inflation-adjusted balance mean?

It is the end balance expressed in today's money. Dividing by (1 + inflation)^years shows what the future amount would buy at today's prices, which is a better guide to your real progress than the nominal number.

Why is the return treated as an effective annual rate?

Investment returns are normally reported as the yearly change in value. Treating 7% as effective means a lump sum grows by exactly 7% a year, whether you contribute monthly or annually. Monthly contributions use the matching monthly rate of about 0.565%.