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What could steady monthly investing grow into?
Enter a starting balance, a monthly contribution, a nominal annual rate and a number of years. The calculator compounds monthly, assumes each contribution lands at the end of the month, and splits the final balance into the money you put in and the growth it produced.
Nominal annual rate compounded monthly, contributions at month end. A projection, not a promise; returns vary and taxes and fees are excluded.
How the balance is built
The starting principal compounds for every month in the horizon. Each monthly contribution is assumed to arrive at the end of the month, so it earns interest from the following month onward. The future value is the compounded principal plus the future value of that stream of contributions.
The monthly rate is the nominal annual rate divided by twelve. Compounding twelve times a year is an assumption, not a universal rule: daily, quarterly or annual compounding would produce a different balance from the same quoted rate. The same arithmetic also covers a lump sum with no monthly contributions.
Contributed money versus growth
Money contributed is simply the opening balance plus every deposit: the monthly amount times twelve times the number of years, plus the principal. Everything above that line is growth, the part produced by compounding rather than by deposits.
The growth share expresses that split as a percentage of the final balance. Over long horizons the share can become large because earlier gains keep earning. Over short horizons, or with a modest rate, deposits usually dominate. Even a small change in the assumed rate shifts the split noticeably. Comparing the two lines is often more useful than staring at the headline balance.
Reading a projection with care
This is a deterministic projection, not a forecast. Real returns vary year by year, and a bad sequence of early losses can leave a portfolio far below a smooth line even if the average return matches. Nothing here guarantees a return or protects the balance from loss.
The model ignores taxes, fund fees, platform charges and inflation. A nominal balance also buys less in the future. Try a range of rates, including a low one, to see how sensitive the result is. Use the output to compare scenarios and to build a savings habit, not as financial advice.
Frequently asked questions
Are contributions made at the start or the end of each month?
At the end. That is the conservative convention, and it means each deposit earns one month less interest than a deposit made at the start of the month.
Is the annual rate nominal or effective?
Nominal, compounded monthly. The effective annual rate is slightly higher: 7% nominal compounded monthly is about 7.23% effective.
Does this include taxes and fees?
No. Fund expense ratios, platform fees and taxes are excluded, so a real account would grow by less than the projection.
Can I use this for a retirement goal?
It is a generic projection. It ignores inflation, withdrawal rules and taxes, so compare it with a range of assumptions before relying on any single number.