How to use this calculator
Choose what you want to solve for at the top:
- End balance shows what your money grows to with the return and contribution you enter.
- Contribution asks for a target amount and tells you how much to add each month or year to reach it.
- Return rate asks for a target and your planned contribution, and tells you the annual return you would need.
Then fill in:
- Starting amount: what you’re investing today. Use $0 if you’re starting fresh.
- Contribution and Every: how much you’ll add, and whether that’s monthly or yearly.
- Expected annual return: a long-run average growth rate. The calculator treats it as an effective annual rate, so 7% means your balance grows exactly 7% over a full year with no contributions.
- Years: how long you’ll keep investing.
- Under More options, choose whether contributions go in at the end of each period (the usual case for money invested from each paycheck) or the beginning.
The result shows how much of your ending balance came from you and how much came from growth. The chart and table follow the balance year by year.
The formula
The ending balance is the starting amount grown for the full term, plus the future value of a series of equal contributions:
- P is the starting amount
- C is the contribution per period
- i is the return per period. For monthly contributions at 7% a year, i = 1.07^(1/12) − 1 ≈ 0.5654% a month
- N is the total number of periods (20 years × 12 = 240)
If you contribute at the beginning of each period, multiply the contribution part by (1 + i), because every deposit gets one extra period of growth.
To solve for the contribution, the calculator rearranges the same formula: C = (goal − P(1 + i)^N) × i ÷ ((1 + i)^N − 1). There’s no algebraic shortcut for the return, so the calculator searches for it, narrowing in on the rate that hits your target to within a fraction of a cent.
Worked example
You invest $20,000 today and add $500 at the end of every month for 20 years, expecting 7% a year.
- The $20,000 alone grows to about $77,394.
- The 240 contributions total $120,000 and grow to about $253,768.
- The ending balance is about $331,162. You put in $140,000, so growth adds about $191,162, or 58% of the final balance.
Now flip it around. To reach $500,000 in the same 20 years at 7%, you’d need about $833 a month. And if you keep the $500 a month but still want $500,000, you’d need an average return of about 10.09% a year, which is a lot to count on.
How the return assumption changes everything
The same plan ($20,000 up front, $500 a month, 20 years) at different average returns:
| Annual return | Ending balance | Monthly contribution to reach $500,000 |
|---|---|---|
| 4% | $225,743 | $1,254 |
| 5% | $255,968 | $1,101 |
| 6% | $290,862 | $961 |
| 7% | $331,162 | $833 |
| 8% | $377,719 | $715 |
| 10% | $493,680 | $509 |
A few points of return make a big difference over two decades. Since you can’t control the return, it’s sensible to plan with a modest one and treat anything better as a bonus.
Time is the lever you control
Holding the start at $20,000 and the return at 7%, here’s what $500 a month becomes, and what it would take each month to reach $1 million:
| Years invested | Balance with $500/month | Monthly needed for $1 million |
|---|---|---|
| 10 | $124,869 | $5,616 |
| 20 | $331,162 | $1,818 |
| 30 | $736,971 | $725 |
| 40 | $1,535,260 | $283 |
Every extra decade roughly doubles the result or more. Starting ten years earlier can cut the monthly amount you need by more than half.
Tips for using your result
- Run more than one scenario. Try a lower return alongside your hopeful one so you know the range.
- Account for inflation. A balance 30 years from now buys less than the same number today. Use a real return, or check the result with the inflation calculator.
- Use tax-advantaged accounts first. A 401(k) with an employer match, or a Roth IRA, lets more of your growth stay invested.
- Planning for retirement? The retirement calculator adds withdrawals, Social Security and life expectancy to the picture.
- Saving in a bank account instead? The savings calculator works with an APY, and the compound interest calculator lets you pick a compounding frequency.
Assumptions and limitations
The calculator applies the same return every year. Real investments rise and fall, and the order of good and bad years matters once you start withdrawing. It doesn’t subtract fund fees, taxes or trading costs, and it assumes every contribution is made on schedule. Treat the result as a projection to plan around, not a forecast.
This calculator is for educational purposes and isn’t investment advice. Past market returns don’t guarantee future results.
Frequently asked questions
How much will I have if I invest $500 a month for 20 years?
At a steady 7% annual return, investing $500 at the end of every month for 20 years grows to about $253,768 from contributions alone. Adding a $20,000 starting amount brings the total to about $331,162. At 5% the same plan reaches about $255,968, which shows how much the return assumption matters.
What rate of return should I assume?
There is no single right number. Many planners use 5% to 7% a year for a diversified stock-heavy portfolio over long periods, and less for bonds or cash. Try a few rates and plan around a result you'd be comfortable with even if returns come in lower.
Does it matter whether I invest at the beginning or end of the month?
A little. Money invested at the start of each period earns one extra period of growth. With $500 a month at 7% for 20 years, investing at the beginning instead of the end adds about $1,400. With once-a-year contributions the gap is larger because each deposit waits a full year.
How do I find the return I need to reach a goal?
Choose Return rate under Solve for, then enter your target, starting amount, contribution and number of years. The calculator searches for the steady annual return that lands exactly on your target. If the answer is well above what markets have historically delivered, more time or bigger contributions are usually more realistic levers.
Is the return in this calculator before or after inflation?
It's whatever you enter. Use a nominal return (such as 7%) to see future dollars, or a real return (nominal minus expected inflation, such as 4% to 5%) to see the result in roughly today's buying power. Our inflation calculator can help you translate between the two.
Are taxes and fees included?
No. The calculator grows your money at the rate you enter. Fund fees and taxes on dividends or gains in a regular brokerage account reduce your actual return, so subtract them from the rate if you want a more conservative projection.
Updated November 2026. Results are estimates for educational purposes and depend on the inputs you provide.