By monthly amount
- $25 a month
- $50 a month
- $100 a month
- $150 a month
- $200 a month
- $250 a month
- $300 a month
- $400 a month
- $500 a month
- $750 a month
- $1,000 a month
- $1,500 a month
- $2,000 a month
- $3,000 a month
Formula: FV = P(1+r)n + PMT × ((1+r)n − 1) ÷ r, with r = annual rate ÷ 12.
For official background on compounding, see the SEC's Investor.gov compound interest calculator.
Worked example
$10,000 left for 20 years at a 7% annual return, compounded monthly, grows to about $40,387. Adding $200 a month as well takes it to about $144,600.
The rule of 72
Divide 72 by the annual rate to estimate how many years money takes to double: about 10 years at 7%, 18 years at 4%. Returns from investments vary year to year; the calculator uses a constant rate as an assumption.
Frequently asked questions
What is compound interest?
Interest earned on both your deposits and the interest already earned.
Does compounding frequency matter much?
A little: at 5%, monthly compounding gives 5.12% a year and daily gives 5.13%.
Should I adjust for inflation?
Subtract expected inflation from the return for a rough figure in today's dollars.