Model how your money grows with recurring contributions, compounding frequency, inflation-adjusted returns, and side-by-side comparisons against simple interest.
Year 30 balance
$914,745
Interest earned
$619,292
Wealth multiplier
3.10×
Raise your monthly savings each year — e.g. salary step-ups.
Goal milestone
Not reached
Increase savings, return, or horizon to hit your goal within 30 years.
Rule of 72
10.3 yrs
Approximate time to double your money at 7% annual return.
Interest share of final balance
67.7%
Effective annual return on capital invested: 3.84%
Real purchasing power
$436,098
Today's dollars after 2.5% annual inflation.
| Year | Opening | Contributions | Interest | Closing | Real value |
|---|---|---|---|---|---|
| 21 | $367,509 | $10,837 | $26,922 | $405,268 | $241,291 |
| 22 | $405,268 | $11,162 | $29,662 | $446,092 | $259,119 |
| 23 | $446,092 | $11,497 | $32,624 | $490,212 | $277,802 |
| 24 | $490,212 | $11,842 | $35,825 | $537,879 | $297,380 |
| 25 | $537,879 | $12,197 | $39,282 | $589,358 | $317,894 |
| 26 | $589,358 | $12,563 | $43,016 | $644,936 | $339,388 |
| 27 | $644,936 | $12,940 | $47,046 | $704,922 | $361,907 |
| 28 | $704,922 | $13,328 | $51,395 | $769,644 | $385,498 |
| 29 | $769,644 | $13,728 | $56,087 | $839,458 | $410,211 |
| 30 | $839,458 | $14,139 | $61,147 | $914,745 | $436,098 |
Compound interest means you earn returns on your previous returns, not just on what you put in. Over long periods, the growth on growth becomes the largest part of your balance — which is why starting early and contributing regularly matters so much.
Compound interest is interest earned on both your original money and the interest it has already earned. Each period's growth is added to the balance, so the next period grows from a larger base.
For a single deposit, the future value is P × (1 + r/n)^(n × t), where P is the principal, r the annual rate, n the number of compounding periods per year and t the number of years. Regular contributions add a series of these terms.
More frequent compounding (monthly instead of yearly) slightly increases the final balance because growth is added sooner. The rate of return and time invested matter far more than frequency.
Divide 72 by your annual return to estimate how many years it takes to double your money. At 8% a year, money doubles in about 9 years.