The power of time
Growth accelerates because each year's interest is added to the balance that earns the next year's interest. That is why starting early matters more than starting big: money invested for 30 years has far longer to compound than money invested for 10.
How this calculator works
It converts the annual return and compounding frequency into an equivalent monthly rate, then, month by month, grows the balance and adds your deposit. Deposits are assumed to be made at the end of each month.
The rule of 72
A quick mental shortcut: divide 72 by the annual percentage return to estimate how many years it takes money to double. At 6% it is about 12 years; at 9% about 8 years.
Be realistic
Investment returns vary year to year and are never guaranteed; savings account rates change. Fees, inflation and taxes reduce what you keep. Treat the result as an illustration, not a forecast.
Frequently asked questions
What return should I assume?
Savings accounts and bonds pay less than stocks have historically, but stocks can fall sharply. Try several rates, including a pessimistic one.
Does it include inflation?
No. To see value in today's money, subtract expected inflation from the return rate.
Is compounding daily much better than monthly?
Only slightly. The rate and time matter far more than the frequency.