# Investment Calculator

> An investment grows by earning returns on both your money and past gains: $10,000 plus $500 a month at 7% a year grows to about $292,465 in 20 years, $162,465 of it growth on $130,000 invested. At 3% inflation, that is $161,931 in today's dollars.

- Interactive calculator: https://calculatorswithsteps.com/investment-calculator
- Category: Financial Calculators
- Last updated: 2026-11-10
- Publisher: Calculators With Steps (calculatorswithsteps.com)

## How to use the investment calculator

1. **Starting amount** – what you invest today. Enter 0 if you are starting from scratch.
2. **Contribution and frequency** – how much you add each month or each year.
3. **Expected annual return** – the average yearly growth you assume, after fund fees.
4. **Years to invest** – how long until you need the money.
5. **Annual contribution increase** (optional) – raise your contribution each year, for example in line with pay rises.
6. **Inflation rate** (optional) – shows the ending value in today's dollars. Set it to 0 to skip.

The result shows the ending balance, how much came from your own money and how much from growth, a yearly chart and a table with the balance in both future and today's dollars.

## How the projection is calculated

The calculator converts the annual return R into the monthly rate that compounds to it, i = (1 + R)^(1/12) − 1, then steps through every month: the balance grows by i, and contributions are added at the end of each month (or at the end of each year for annual contributions). With a constant contribution this matches the standard formulas:

**FV = P(1 + R)^t + C × [(1 + i)^n − 1] ÷ i**

- **P** = starting amount
- **C** = contribution per period, **n** = number of contributions
- **R** = annual return, **i** = return per contribution period
- **t** = years

To express the result in today's dollars, divide by (1 + inflation)^t.

## Worked example

$10,000 to start, $500 a month, 7% a year for 20 years, with 3% inflation:

| Item | Value |
| --- | --- |
| Starting amount after 20 years | $38,696.84 |
| Total contributed | $130,000 |
| **Ending balance** | **$292,465** |
| Growth from returns | $162,465 |
| In today's dollars | $161,931 |
| Real return | 3.88% a year |

More than half of the final balance is growth rather than money you put in. Most of it arrives late: the balance passes $105,000 after 10 years and then nearly triples over the next 10.

## How the return assumption changes the result

The same $10,000 plus $500 a month over 20 years:

| Annual return | Ending balance | Growth |
| --- | --- | --- |
| 5% | $229,435 | $99,435 |
| 7% | $292,465 | $162,465 |
| 9% | $375,470 | $245,470 |
| 10% | $426,405 | $296,405 |

A few percentage points change the outcome by more than $100,000. Fees work the same way in reverse: a 1% annual fee turns a 7% return into roughly 6%. Low-cost index funds keep more of the return in your account.

## Nominal vs. real returns

The ending balance is in future dollars. A dollar in 20 years will buy less than a dollar today, so the calculator also divides by cumulative inflation to show the value in today's money. In the example, $292,465 in 20 years has the buying power of about $161,931 now. The same idea gives the real return: (1 + 7%) ÷ (1 + 3%) − 1 = 3.88% a year. Planning with real values keeps goals honest. If you need $50,000 a year of today's spending in retirement, compare that with a today's-dollars balance, not the larger future-dollar figure. The [inflation calculator](https://calculatorswithsteps.com/inflation-calculator) converts any amount between today and a future year.

## Investing tips

- **Start with time, then amount.** Investing for twenty years instead of ten adds $60,000 of contributions in the example, but nearly triples the ending balance.
- **Automate contributions** and raise them when your income rises. A 3% yearly increase adds about $65,577 to the 20-year result.
- **Use tax-advantaged accounts first.** In the U.S., a 401(k) or IRA can shelter growth from tax. The [401(k) calculator](https://calculatorswithsteps.com/401k-calculator) includes employer matching.
- **Think in real terms.** A projection in today's dollars is easier to plan with. The [inflation calculator](https://calculatorswithsteps.com/inflation-calculator) shows how prices change over time.
- **Check past performance properly.** To measure what an investment actually returned, use the [ROI calculator](https://calculatorswithsteps.com/roi-calculator) or the [CAGR calculator](https://calculatorswithsteps.com/cagr-calculator).

Returns from stocks and bonds are not guaranteed and do not arrive evenly. A projection with a steady return is a planning tool, not a promise.

## Frequently asked questions

### How do I calculate investment growth over time?

For a single amount use FV = P × (1 + R)^t. $10,000 growing at 7% a year for 20 years becomes 10,000 × 1.07^20 = $38,696.84. Regular contributions are added with the future value of an annuity, which this calculator does month by month.

### How much will I have if I invest $500 a month?

With $10,000 to start and $500 a month at a steady 7% annual return, you would have about $105,197 after 10 years, $292,465 after 20 years and $660,849 after 30 years. Actual returns vary from year to year.

### What rate of return should I use?

There is no single right number. Use a figure that matches your mix of stocks, bonds and cash, and test a range. On the example, 5% gives $229,435 after 20 years and 9% gives $375,470, so the assumption matters a lot.

### What does the value in today's dollars mean?

It is the future balance divided by cumulative inflation, so you can compare it with prices now. At 3% inflation, $292,465 in 20 years buys about what $161,931 buys today. The real return is (1.07 ÷ 1.03) − 1 = 3.88% a year.

### Does increasing my contribution each year help?

Yes. Raising the $500 monthly contribution by 3% a year lifts the 20-year value from $292,465 to about $358,042. The monthly amount reaches $877 in the final year.

### Is it better to invest monthly or once a year?

Monthly investing gets money working sooner. $500 a month for 20 years at 7% ends at $292,465, while $6,000 invested at the end of each year ends at $284,670, about $7,795 less.

### How long does it take to double an investment?

Divide 72 by the annual return. At 7% the rule of 72 gives about 10.3 years; the exact figure is 10.2 years.

## Sources

- [Wikipedia – Compound interest (future value formulas)](https://en.wikipedia.org/wiki/Compound_interest)
- [Wikipedia – Rule of 72](https://en.wikipedia.org/wiki/Rule_of_72)

> Disclaimer: results are estimates for information and education, not financial advice. Confirm important decisions with a qualified professional.