How to use this investment calculator
Enter what you have invested today, how much you plan to add each month, the average annual return you expect, and how many years you will stay invested. The calculator compounds your balance monthly and shows three numbers that matter: what you will have contributed, how much came from investment growth, and what the final balance is worth after inflation. Every change updates instantly, and the address bar keeps your inputs so you can bookmark a scenario or send it to someone.
- Starting amount – money already invested, such as an existing brokerage or retirement balance.
- Monthly contribution – the amount you add at the end of each month.
- Annual return – your assumed average yearly return before inflation.
- Inflation – used only to translate the final balance into today's purchasing power.
- Yearly raise – optionally increase your monthly contribution each year, for example as your salary grows.
The formula behind the results
The calculator converts your annual return into a monthly rate and applies it to your balance every month, then adds that month's contribution. For a fixed monthly contribution this is equivalent to the standard future-value formula for a lump sum plus an ordinary annuity:
FV = P × (1 + r)n + PMT × [((1 + r)n − 1) / r]
where P is the starting amount, PMT the monthly contribution, r the monthly rate (annual return ÷ 12) and n the number of months. The inflation-adjusted balance divides the result by (1 + inflation)years. When you set a yearly raise, the monthly amount is increased once at the end of every 12 months, so the closed-form formula no longer applies and the month-by-month simulation is used directly. See our methodology for details.
Worked examples
Starting early vs. starting late
Investing $500 a month at a 7% average return for 30 years builds about $609,985 from $180,000 of contributions. Waiting ten years and investing the same $500 a month for only 20 years ends with about $260,463. The extra decade of contributions costs just $60,000, yet it adds $349,522 to the final balance — that is compounding at work.
Raising contributions with your income
Start with $10,000, add $300 a month and earn 6% a year for 25 years: you end with about $252,548. Increase the monthly contribution by just 3% each year — roughly in line with typical pay raises — and the result grows to about $321,657.
How much does the rate of return matter?
Small differences in annual return compound into large differences over decades. Here is $10,000 plus $500 a month over 25 years at different average returns:
| Annual return | Total contributed | Final balance | Growth |
|---|---|---|---|
| 4% | $160,000 | $284,202 | $124,202 |
| 6% | $160,000 | $391,147 | $231,147 |
| 8% | $160,000 | $548,915 | $388,915 |
| 10% | $160,000 | $783,986 | $623,986 |
That is also why investment costs matter: a fund charging 1% a year instead of 0.05% effectively moves you down almost a full row in this table. Low-cost index funds keep more of the return compounding for you.
Limits of any investment projection
Real markets do not deliver a smooth return every year. A portfolio averaging 7% might gain 25% one year and lose 15% the next, and the order of those returns matters — especially close to retirement, when withdrawals begin. Treat the result as one plausible path, not a forecast. Running a conservative, a middle and an optimistic rate gives a more honest picture than a single number. If you invest a fixed amount on a schedule, the dollar cost averaging calculator shows how regular buying smooths your average cost, and the dividend calculator projects income from dividend-paying stocks and ETFs.
Frequently asked questions
What rate of return should I use in an investment calculator?
It depends on what you invest in. Broad US stock index funds have historically returned roughly 10% a year before inflation over very long periods, but with large swings and long stretches of much lower returns. Many planners use 5–7% for a diversified stock-heavy portfolio to stay conservative, and lower rates for bond-heavy or cash portfolios. Try several rates to see a range of outcomes rather than relying on one number.
Does this investment calculator account for inflation?
Yes. Enter an expected inflation rate and the calculator shows your final balance in today's dollars alongside the nominal figure. The default of 2.5% is close to the long-run US average and the Federal Reserve's 2% target plus a small margin.
Are contributions made at the beginning or end of each month?
This calculator assumes contributions at the end of each month and monthly compounding of your annual return. If you want to model start-of-month deposits or a different compounding frequency, use the compound interest calculator.
Does the calculator include taxes and fees?
No. Results are before taxes, fund expense ratios and advisory fees. To approximate fees, subtract them from your expected return — for example, use 6.8% instead of 7% for a fund charging 0.2% a year. Tax-advantaged accounts like a 401(k) or IRA can defer or eliminate taxes on growth.
Is my data saved anywhere?
No. All calculations run in your browser. The numbers you enter only appear in the page address so you can bookmark or share a specific scenario.
Not financial advice. These figures are hypothetical and assume a constant rate of return. Real investments go up and down, past performance does not predict future results, and taxes and fees vary. Consider speaking with a licensed financial professional before making investment decisions. See our full disclaimer.