How this calculator works
Interest is compounded monthly and deposits are added at the end of each month. Here r is the annual return divided by 12 and n is the number of months.
future value = start × (1 + r)n + deposit × ((1 + r)n − 1) ÷ r
Real investment returns are not steady, so treat the result as an illustration, not a promise.
Worked example
Using sample inputs for a $5,000 starting balance, $200 a month, a 7% annual return and 20 years:
Future value$124,379.03
Total you put in$53,000.00
Interest earned$71,379.03
Common questions
What is the Rule of 72?
It is a quick estimate of how long money takes to double: divide 72 by the annual return. At 6% it takes roughly 12 years.
What return rate should I use?
Savings accounts pay far less than long-term stock market averages, and market returns are never guaranteed. Try a few different rates to see the range of outcomes.
Does adding more each month matter?
Yes. Regular deposits often add more to the final balance than the starting amount, especially over shorter periods.