CalcMyFin

Investing & Growth

Investment Growth Calculator

See how a starting balance and regular monthly investments could grow when returns are reinvested. The chart shows how much of your future balance comes from your own contributions and how much from growth.

  • Free, no sign-up
  • Private: runs in your browser
  • Updated September 2026

Inputs

$
Amount invested or saved today.
$
Assumed contribution made throughout the year.
%
yr
How often gains are reinvested. Monthly is a good approximation for most funds.

How to use the investment growth calculator

  1. Enter your starting amount and how much you'll invest each month.
  2. Add the average yearly return you expect from your investments.
  3. Choose how many years, and how often returns are added to your balance.

How it's calculated

For a starting amount P, expected yearly return r added n times per year for t years:

A = P(1 + r/n)nt

Monthly contributions are added along the way and grow the same way. The calculator steps through every period, so gains are reinvested and start earning returns of their own.

Example

Start with $10,000, invest $300 a month and earn an average 7% a year, reinvested monthly. After 20 years you'd have about $196,665. You put in $82,000, so roughly $114,665 came from investment growth.

Tips

  • Time matters more than amount. Starting 10 years earlier can double your final balance.
  • The Rule of 72: divide 72 by your expected return to estimate how many years it takes money to double.
  • Automate monthly investing so it happens before spending.
  • Returns vary year to year and can be negative. Use a conservative figure for planning.

Frequently asked questions

How does investment growth snowball?
When gains are reinvested, they start producing gains of their own. Early on, most of your balance is your own money; over long periods growth can become the larger part, which is why starting early matters.
What return should I use?
It depends on what you invest in. For a long-term, diversified stock portfolio many people plan with a conservative 5–7% average, but returns are never guaranteed and can be negative in any given year.
Does it matter how often returns are added?
A little. More frequent reinvestment grows slightly faster at the same yearly return, but the effect is small compared with your return, contributions and time.
Is this a guaranteed result?
No. The calculator assumes a steady average return to show the shape of long-term growth. Real markets rise and fall, so treat the result as one possible scenario.
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Sources

This calculator provides educational estimates only and is not financial, tax, legal or investment advice. Results depend on the assumptions you enter; actual market prices, returns and tax rules may differ.