About the investment calculator
An investment goal has four moving parts: how much you start with, how much you add, the return you earn and how long you wait. Fill in all but one, pick the matching tab and the calculator solves for the missing piece.
The Return Rate tab uses a numerical search, because the rate cannot be isolated with a simple formula. If no realistic rate can reach your goal, or the goal cannot be reached within 100 years, the calculator says so instead of guessing.
Returns are not guaranteed. Use a rate you consider realistic and remember that inflation reduces what the future money will buy.
Formula
- End amount = S × (1 + i)^m + C × ((1 + i)^m − 1) ÷ i
- S = starting amount, C = contribution per period, i = rate per period, m = number of periods
- Contribution = (Goal − S × (1 + i)^m) ÷ (((1 + i)^m − 1) ÷ i)
Example
Starting with $20,000 and adding $500 each month for 10 years at a 6% return (compounded annually) ends at $117,053.68. To reach $150,000 instead you would need to add about $702.78 a month.