How much will my investment be worth in 10 or 20 years?
No one can tell you in advance, but you can see what each assumption implies. $10,000 plus $500 a month, less a 0.1% fee, reaches $98,526 in 10 years and $255,485 in 20 at an assumed 6%. At 8%, it reaches $110,934 and $326,674. That spread is the point.
| Assumed return | After 10 years | After 20 years | After 30 years |
|---|---|---|---|
| 4% | $87,617 | $201,364 | $368,063 |
| 6% | $98,526 | $255,485 | $533,776 |
| 8% | $110,934 | $326,674 | $787,804 |
| 10% | $125,039 | $420,451 | $1,179,045 |
The contributions are the part you control. Over 20 years you'd put in $130,000 under every row. Everything above that depends on markets, which you don't control.
Why steady-return projections mislead
A steady return runs high, because swings lower what you actually compound at. Suppose an investment gains 20% one year and loses 10% the next. The simple average is 5%. But $10,000 becomes $10,800, which is a compound return of only 3.92% a year.
That's why the simulated median here is $360,662, about 18% below the steady projection of $438,313, even though both use about the same average return. The headline number isn't the middle of the range. It sits well above it.
The order of returns matters once you're adding money. Start with $10,000 and add $6,000 at the end of each of three years. Returns of -25%, 10%, 30% end at $33,105. The same returns in reverse order end at $26,175. Early losses hurt less when you have little invested, and late ones hit your largest balance. A straight line can't show this.
How to read the simulated range
The chart shows three lines from 600 simulated market paths. The middle line is the median, so half the paths end above it and half below. The other two are the 10th and 90th percentiles, which means 8 in 10 paths land between them. It also means 1 in 10 ends below the low line, and the true worst case isn't shown.
| Year | You put in | Weak markets (10th percentile) | Median | Strong markets (90th percentile) | Steady projection |
|---|---|---|---|---|---|
| 5 | $40,000 | $36,254 | $47,656 | $65,584 | $49,461 |
| 10 | $70,000 | $66,952 | $98,159 | $145,991 | $104,531 |
| 15 | $100,000 | $103,800 | $164,223 | $270,927 | $181,384 |
| 20 | $130,000 | $145,441 | $256,318 | $463,070 | $288,637 |
| 25 | $160,000 | $199,091 | $360,662 | $696,965 | $438,313 |
Look at year 10. The low line is $66,952, below the $70,000 you'd have put in. Ten years of saving can still leave you behind on paper in a weak stretch. Time narrows the risk of ending below your deposits in this model, but it doesn't remove it.
Know what the model assumes. Each year's return is drawn independently from a lognormal distribution using your return and volatility inputs. It's seeded, so the same inputs always show the same range. Real markets can have long slumps and extreme years that this doesn't capture, and the range is only as good as your assumptions. Raise Market volatility under More options, or try the Return 1% lower button, to test how much your plan depends on them.
How much do investment fees really cost?
More than the percentage suggests. With these inputs, moving from a 0.1% fee to 1% costs $61,370 over 25 years. As the SEC explains, you lose the fee and also any return that money would have earned.
| Annual fee | Final value | Cost compared with no fee |
|---|---|---|
| 0% | $445,795 | $0 |
| 0.1% | $438,313 | $7,482 |
| 0.25% | $427,351 | $18,444 |
| 0.5% | $409,754 | $36,041 |
| 1% | $376,943 | $68,852 |
| 1.5% | $347,066 | $98,729 |
The SEC's own fee bulletin uses $100,000 at 4% for 20 years. Using this site's math on those inputs, it ends at $219,112 with no fee, and at $208,413 with 0.25%, $198,211 with 0.5%, $179,213 with 1%.
Add up everything you pay. That can include a fund's expense ratio, an adviser's annual fee, sales loads, commissions, and 401(k) plan fees, which come on top of the expenses of the funds in the plan. A fund's expense ratio is in its prospectus, listed as total annual fund operating expenses, and FINRA's Fund Analyzer compares funds and ETFs. Enter the total in Annual fees.
What is left after taxes and inflation?
In today's dollars at 2.5% inflation, the $438,313 projection buys what $236,422 buys now. If this is a taxable account and you sell it all at the end, a 15% tax on the $278,313 gain takes $41,747. Set Capital gains tax at sale to 0 for a Roth account.
That tax setting is a simplification. The IRS taxes gains on assets held more than a year at long-term rates that depend on your income, and short-term gains as ordinary income. Dividends are generally taxable in the year you receive them, so use Yearly tax on growth to model that drag in a taxable account. A tax professional can help you with real numbers, and the IRA calculator and 401(k) calculator cover tax-advantaged accounts.
What this calculator cannot tell you
It can't tell you what to buy or what markets will do, and it doesn't try. Mutual funds aren't guaranteed or insured by the FDIC or any other government agency, and you can lose some or all of the money you invest. The SEC also notes that past performance doesn't predict future returns.
Your time horizon matters too. The SEC says investors with shorter horizons may prefer less volatile investments. If you'll need this money within a few years, run the numbers in the savings calculator too. If you want personal advice, ask how the person is paid and check that they're registered using the free search tool on Investor.gov. The SEC calls registration the most important thing to check before you hire someone.
Common questions
What is a Monte Carlo investment calculator?
It runs many simulated futures with randomly drawn returns and reports the spread of results. This one runs 600 paths in yearly steps. It gives you a sense of range, not odds you can count on, because the inputs are your assumptions.
What does annual return on your money mean in the results?
It's a money-weighted return: the single yearly rate that turns your deposits, each at its own date, into the final value after fees. With the default inputs it's 6.89%, which is your assumed return after fees. It's most useful when you add taxes or change contributions, because it stays a fair single rate where a simple gain percentage would mislead.
Can I use this for an S&P 500 index fund?
Yes, as a what-if. Enter your own return assumption and the fund's expense ratio as the fee. This site doesn't suggest a return for any fund or index, and past results won't tell you what's next. Try a low return alongside the one you hope for.
Should I include dividends in the expected return?
Yes, if you reinvest them. The return field is total return, so it should include price changes and reinvested dividends together. Don't add them twice. To model the tax on dividends in a taxable account, use Yearly tax on growth.
What if I only invest a lump sum?
Set Monthly contribution to 0, or use the preset. $100,000 at an assumed 7% less a 0.1% fee projects to $379,302 in 20 years on a steady path. With no new deposits, the order of returns doesn't change the ending value, but the size of the swings still does, so check the range too.
Does this show withdrawals?
No. It only models money going in. The retirement calculator handles withdrawals and how long a balance lasts.
Sources
- How fees and expenses affect your investment portfolio · U.S. Securities and Exchange Commission
- Mutual funds · U.S. Securities and Exchange Commission, Investor.gov
- Asset allocation and diversification · U.S. Securities and Exchange Commission, Investor.gov
- Working with an investment professional · U.S. Securities and Exchange Commission, Investor.gov
- Topic no. 409: Capital gains and losses · Internal Revenue Service
- Topic no. 404: Dividends · Internal Revenue Service