The chart separates principal from investment growth. Early in the projection, new deposits usually drive most of the balance; later, growth can become the larger component. That transition illustrates why time and consistency matter.
The calculator compounds a smooth monthly rate, while real returns arrive unevenly and fees reduce the balance. Do not use an equity-like return for cash needed within a few years.
Long-run compounding on recurring contributions, in real terms
Your starting amount and monthly contributions compound month by month at your expected return. Contributions and balance are charted separately so you can see when growth overtakes what you put in — and the inflation-adjusted value alongside it.
The chart separates principal from investment growth. Early in the projection, new deposits usually drive most of the balance; later, growth can become the larger component. That transition illustrates why time and consistency matter.
The calculator compounds a smooth monthly rate, while real returns arrive unevenly and fees reduce the balance. Do not use an equity-like return for cash needed within a few years.
UNDERSTAND THE NUMBERS
Fixed educational example · independent of your inputs above. $ means US dollars; these are not current rate quotes or return forecasts.
Start at $0 and contribute $500 at each month-end for 20 years. Total deposits are $120,000. These constant annual returns are sensitivity scenarios, not forecasts; taxes and fees are excluded.
| Annual return | Ending balance | Growth above deposits |
|---|---|---|
| 4% | $181,921 | $61,921 |
| 6% | $226,719 | $106,719 |
| 8% | $284,500 | $164,500 |
The contribution schedule is identical in all three rows. Only the assumed return changes. This makes the gap a measure of dependence on investment performance, rather than evidence that the largest number is attainable. A plan that works only in the highest-return row has less room for disappointment.
EconoPi treats the input as an effective annual return: the monthly rate is (1 + annual return)^(1/12) − 1. Dividing the annual rate by 12 instead produces a different result. End-of-month deposits also have one less month of growth than beginning-of-month deposits.
Use the middle scenario, then increase the monthly contribution by $100 without raising the return. Compare that improvement with extending the horizon by five years. Savings and time are separate planning levers.
See how annual fees change growth →Prepared by EconoPi · examples and explanations reviewed September 19, 2026. Tables are our calculations under stated assumptions, not forecasts or recommendations by the referenced organizations.
With monthly compounding, A = P(1+r)^n + M × ((1+r)^n − 1) / r, where r is the monthly return and n the number of months.
Divide 72 by the annual return for a rough doubling time — about 9 years at 8%.
Starting from zero, $500 deposited at each month-end for 20 years grows to about $284,500 at an effective annual return of 8%, before fees and taxes. Total deposits are $120,000.
Nominal dollars lose purchasing power. At 2.5% inflation, a balance 20 years out is worth about 61% of its face value today.
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