How much to invest per month to become a millionaire

Three inputs decide almost the whole answer, and they matter in roughly this order.

• Years until you want the money. Compounding is exponential, so the last decade of a 40-year plan adds more dollars than the first three decades of contributions. Going from 30 years to 40 years at 8% drops the monthly requirement from about $710 to about $310.
• The average annual return. The difference between 6% and 10% over 30 years is the difference between $1,026 and $485 a month. Nobody knows the future return, so the honest approach is to look at a range rather than one number.
• What you have already saved. A starting balance compounds alongside the new money. With $50,000 already invested, the 20-year figure at 8% falls from $1,757 to about $1,348 a month. With $100,000, it falls to about $938.

Fees and taxes act on the return. A portfolio earning 8% before a 1% annual fee earns 7% after it, and over 30 years that single point moves the monthly requirement from $710 to $855.

The long-run reference most people reach for is the S&P 500. Using the annual returns in NYU Stern professor Aswath Damodaran's historical return series (updated January 2026), the index returned about 10.0% a year compounded, with dividends reinvested, from 1928 through 2025. The simple average of the yearly returns was higher, about 11.9%, but the compounded figure is the one that matches what a balance actually does.

That 98-year record includes 26 losing years. Even the worst 30-year stretch in the series, 1929 through 1958, compounded at about 8.0% a year. The best, 1970 through 1999, compounded at about 13.6%. Those figures are before fees, before taxes and before inflation, and they describe one country's large-company stocks over a period that turned out well for them.

A common planning choice is 6% to 8% for a diversified stock-heavy portfolio, leaving room for fees, a bond allocation and decades that look more like the weak end of history than the average. The tables below show 6%, 7%, 8% and 10% side by side. More detail on the historical figures is in the average stock market return statistics.

Each figure assumes the same amount invested at the end of every month, returns compounding monthly at the stated annual rate, and no starting balance.

Read down any column and the effect of time is plain. At 8%, someone with 40 years needs $310 a month, and someone with 20 years needs $1,757, more than five times as much, to reach the same balance.

Take a 35-year-old who wants $1 million by 65 and assumes 8% a year.

• An 8% annual return compounds to a monthly rate of 1.08 raised to the power of 1/12, minus 1, which is about 0.643%.
• Thirty years is 360 monthly contributions.
• The future value of a monthly payment P is P × ((1 + i)ⁿ - 1) ÷ i. With i = 0.00643 and n = 360, the multiplier is about 1,408.
• Setting P × 1,408 = $1,000,000 gives P ≈ $710 a month.

Over those 30 years the investor puts in about $255,600 of their own money. The other $744,000 or so is growth. Shorten the window to 20 years and contributions rise to about $421,800 of the $1 million, because there is less time for growth to do the work.

The same formula answers the reverse question. Investing a fixed $1,000 a month at 8% reaches $1 million in about 26 years. At $500 a month it takes about 34 years, at $250 about 43 years, and at $2,000 about 19 years.

For the mechanics of why growth accelerates, see what is compound interest and the compound interest statistics.

The same table reorganized by age, at 8% and 6%, with nothing saved at the start.

Waiting from 25 to 35 more than doubles the monthly amount at 8%, from $310 to $710. That gap is the usual argument for starting early with a small amount rather than later with a large one, and it is covered further in when should I start investing.

The same math runs in one step for a single deposit. At 8% a year, about $46,000 invested once today grows to $1 million in 40 years with nothing added. Over 30 years the one-time amount is about $99,400, and over 20 years about $214,500.

Most people combine the two: whatever is already invested counts as the lump sum, and the monthly figure covers the rest. That is why the starting balance cut the 20-year requirement from $1,757 to $938 a month in the earlier example once $100,000 was already in place.

Every figure above is in future dollars. Prices rise in the meantime, so the million you reach is worth less than a million today.

At an assumed 3% inflation rate, $1 million in 20 years buys roughly what $554,000 buys now. In 30 years it is about $412,000, and in 40 years about $307,000.

To hit $1 million of today's purchasing power, one approach is to run the formula with a return after inflation. If an 8% portfolio return and 3% inflation leave about 5% in real terms, reaching a real $1 million takes about $1,226 a month over 30 years and about $675 a month over 40 years. Another approach is to start from the nominal figure and raise the monthly amount each year in line with pay.

The Federal Reserve's 2022 Survey of Consumer Finances puts the median US family's net worth at $192,900 and the mean at $1,063,700, with the mean pulled up by the wealthiest households. Families between the 75th and 90th percentiles of net worth had a median of $1,036,200, which places a $1 million net worth inside the top quarter of US families, near the middle of that band. The same survey found 54.3% of families held retirement accounts, with a median balance among holders of $86,900.

Net worth includes home equity, so a household can be a millionaire on paper with far less invested. The figures in this guide are about invested assets only. Fidelity's Q2 2026 retirement analysis reported an average 401(k) balance of $155,800 and a total savings rate of 14.4% of pay, employee and employer combined. More on who reaches seven figures is in the millionaire statistics and net worth by age.

Tax-advantaged accounts shrink the drag that taxes put on the return. For 2026 the IRS set the employee 401(k) limit at $24,500, with an $8,000 catch-up from age 50 and $11,250 for ages 60 to 63. The IRA limit is $7,500, plus a $1,100 catch-up at 50.

Put in monthly terms, a full 401(k) contribution is about $2,042 a month and a full IRA is $625. Investing the full 401(k) amount for 20 years at 8% grows to about $1.16 million, before any employer match. An employer match counts toward the monthly figure too, since it is money invested on your behalf.

Above those limits, or for goals before retirement age, a taxable brokerage account has no contribution cap and no age rules. Many investors who automate a monthly amount use a low-cost index fund; see what is an index fund and what is dollar-cost averaging.

Walnut is an AI investing app that sits on top of the brokerage account you already have. It does not hold or move your money.

1. Connect your brokerage

Link the account read-only and Walnut reads your actual holdings and balances. If you do not have an account yet, Public and Robinhood are two places to open one. Your starting balance is the third input in the formula, and it can change the monthly figure by hundreds of dollars.

2. Set the goal

Add a goal such as $1 million by a target date. Walnut projects whether your current balance is on pace and keeps that projection current as your holdings change.

3. Compare against the S&P 500

The dashboard shows how your holdings have done against the S&P 500 over the same window, which is a quick check on whether the return you assumed in the plan is the return you are getting.

4. Build a basket and set a recurring investment

A basket is a set of holdings with target weights. You can set a recurring investment into it, a fixed amount on a schedule split across those weights. It spends cash that is already in your brokerage account; you or your broker's own transfer puts the money there. Orders are placed at your broker, and only under a plan you set up and can pause.

5. Ask the assistant

The assistant can read your portfolio and rerun the numbers with you: what a different return assumption does to the monthly figure, or how far a current balance gets on its own.

• Planning with the best-case return. The last ten years of the S&P 500 compounded at about 14.7% a year in the same NYU Stern data. Plugging that into a 30-year plan gives a monthly figure that leans on the luckiest decade in recent memory.
• Forgetting inflation. A nominal $1 million in 40 years is a very different goal from $1 million of today's spending power.
• Ignoring fees. One percentage point of annual cost raised the 30-year monthly requirement from $710 to $855 in the example above.
• Stopping in a downturn. The formula assumes every monthly payment goes in. Pausing contributions during a falling market skips the months when each dollar buys the most.
• Leaving an employer match unclaimed. A match is part of the monthly figure, so missing it means making up the difference from your own pay.
• Holding the amount flat for decades. A contribution that rises with income reaches the target sooner, and partly offsets inflation.

Historical S&P 500 returns: Damodaran, NYU Stern, Historical Returns on Stocks, Bonds and Bills, updated January 2026; compounded and rolling figures are calculated from its annual returns. Net worth and retirement account figures: Federal Reserve Bulletin, Changes in U.S. Family Finances from 2019 to 2022. 2026 contribution limits: IRS. 401(k) balances and savings rate: Fidelity Q2 2026 Retirement Analysis. All projections are illustrations using the stated assumptions, not forecasts. Walnut is informational and is not an investment adviser. This guide is educational and not personalized financial advice.