How the projection is built
Two engines drive the balance: your starting amount, which compounds on its own for the whole period, and your monthly contributions, each of which compounds from the day it lands until the end. The calculator adds the two streams together every month at your assumed return.
Because later contributions have less time to grow, the early deposits do most of the heavy lifting. That is why beginning sooner — even with smaller amounts — usually beats starting later with larger ones.
Reading the results
Future value is the projected ending balance. Total contributions is everything you personally put in (starting amount plus all monthly deposits), and total interest is the growth layered on top.
The line chart shows the balance climbing year by year, while the donut compares how much of the final pot came from your own money versus investment returns. Over long horizons the returns slice tends to overtake the contributions slice.
Levers that change the outcome
Small adjustments compound into large differences over time:
- Raise the monthly contribution — the most reliable lever you fully control.
- Extend the time horizon, which gives every dollar more periods to compound.
- Keep costs low; fees quietly subtract from the return you actually earn.
Caveats
The projection assumes a constant average return and ignores taxes, fees, and inflation. Real markets move in fits and starts, and a string of poor early years can leave you below this line. Use the result for planning, not as a precise forecast.
Formula
r = annualRate/100/12; n = years×12; fv = P·(1+r)ⁿ + C·(((1+r)ⁿ − 1)/r)Frequently asked questions
- Are returns guaranteed?
- No. Market returns vary year to year. This projection assumes a constant average annual return, so treat it as an estimate, not a promise.