How much should I invest per month?

There is no single official number for monthly investing, but two rules of thumb show up again and again, and they land close together.

The first is Fidelity's savings guideline: save at least 15% of pre-tax income each year for retirement, including any employer contribution, starting at 25 and retiring at 67. Fidelity's own footnotes raise the figure to 18% for someone starting at 30 and 23% for someone starting at 35, assuming nothing saved yet.

The second is the 50/30/20 budget, popularized by Elizabeth Warren and Amelia Warren Tyagi in All Your Worth. It splits take-home pay into 50% for needs, 30% for wants and 20% for savings and debt repayment. Twenty percent of take-home pay and 15% of gross pay usually land close together for a typical earner (on a $60,000 salary, $800 versus $750 a month), which is why the two rules agree in practice.

The 15% figure is about retirement alone. Investing for a house, a child's education or simply a larger cushion sits on top of it, which is why many planners describe 20% as the fuller target.

Most households invest less than either rule suggests. The Bureau of Economic Analysis put the personal saving rate at 4.1% of disposable income in August 2026. That figure counts all saving across the economy, not just money put into the market, so the share actually invested each month is lower still.

The BLS Consumer Expenditure Survey for 2024 shows why. The average household had $104,207 of income before taxes and spent $78,535. Housing alone took $26,266, transportation $13,318 and food $10,169. Personal insurance and pensions, the line that includes Social Security payroll tax and retirement plan contributions, came to $9,797. After income taxes, there is not much left over for the average household, which is the honest starting point for any monthly target.

The gap between 4% and 15% is not a moral failing. It mostly reflects what a household has left after the fixed costs above, and it is the reason the monthly number is usually built up in steps rather than set once. The personal savings rate statistics page has the longer history.

What comes before investing

A common sequence runs: claim the full employer match on a 401(k), clear credit card and other high-interest debt, build an emergency fund of three to six months of expenses, then raise the monthly investment. Investing while carrying a 22% credit card balance means earning an uncertain market return while paying a certain one that is far higher. How much do I need in an emergency fund covers the cushion step.

Your goals and when you need the money

Money needed within about five years, such as a down payment, is often kept out of stocks entirely because a bad year could arrive just before it is needed. The monthly figure that goes into the market is usually the long-horizon part: retirement, a child's college in 15 years, or general wealth building.

Your income and how steady it is

A salaried worker can set a fixed amount and leave it. Someone with commission or freelance income often invests a percentage of each payment instead, so a lean month does not force a skipped contribution or a dip into savings.

How late you are starting

Every decade of delay roughly doubles the monthly amount needed to reach the same balance at the same age. The table further down shows the arithmetic, and when should I start investing covers the timing question on its own.

Which accounts you use

The same $500 goes further in a 401(k), IRA or HSA than in a taxable account, because growth is sheltered from tax each year. The account choice does not change the number you set aside, but it changes how much of it you keep.

Take someone earning $60,000 before tax who brings home about $4,000 a month. Under 50/30/20, the savings and debt slice is 20% of $4,000, or $800 a month. Under Fidelity's guideline, 15% of $60,000 is $9,000 a year, or $750 a month, and an employer match counts toward it.

Suppose their employer matches 4% of pay, or $200 a month. Their own contribution to reach 15% is $550 a month, with the match bringing the total to $750. The remaining $250 from the 20% slice can go to an emergency fund until it is full, then to an IRA or a taxable brokerage account.

Now the growth. Assume 5% a year after inflation, compounded monthly, so the results are in today's dollars. The future value of a level monthly contribution is the payment times ((1 + r)ⁿ - 1) / r, where r is the monthly rate (0.05 / 12) and n is the number of months.

For $750 a month over 35 years, that is $750 x ((1 + 0.05/12)⁴²⁰ - 1) / (0.05/12), which works out to about $852,000 in today's money. Total contributions were $315,000 ($750 x 12 x 35), so more than half the ending balance is growth.

Drop the assumed return to 4% after inflation and the same contributions reach about $685,000. One point of return over 35 years moves the result by about a fifth, which is why any projection is a range, not a promise. The average stock market return page has the long-run history behind assumptions like these.

The table holds the worked example's assumption (5% a year after inflation, compounded monthly) and shows the result in today's dollars. A 7% assumption, closer to a nominal figure before inflation, is shown in the last row for $500 a month so the two framings can be compared.

Two patterns stand out. The last decade adds more than the first two combined, because compounding works on the balance as well as the new money. And a modest amount started early tends to beat a larger amount started late: $500 a month from 25 to 65 reaches about $763,000, while starting at 35 reaches about $416,000. To close that gap from 35, the monthly figure would have to rise to about $917.

The compound interest statistics page has more examples of the same math.

For many people the realistic path to 15% runs through a lower figure first. A step-up plan sets a starting amount and raises it on a fixed rule, such as $50 more a month each year or one percentage point of pay with each raise.

Using the same 5% after-inflation assumption: $300 a month held flat for 30 years grows to about $250,000 in today's dollars. Start at the same $300 but add $50 a month each year, so the contribution reaches $1,750 in the final year, and the balance comes to about $703,000. The step-up plan never asked for a large amount early on, when it would have been hardest to find.

Many 401(k) plans offer this as an automatic feature, often called auto-escalation, which raises the deferral rate by a point each year until it hits a cap. Outside a workplace plan, the same effect comes from changing a recurring transfer once a year on a fixed date.

The same two rules, put in dollars. The take-home column is a rough illustration, since taxes vary by state and by what comes out of each paycheck.

The tax-advantaged ceilings matter at the top of the table. For 2026 the IRS set the 401(k) employee deferral limit at $24,500 (about $2,042 a month), with an $8,000 catch-up from age 50 and $11,250 for ages 60 to 63. The IRA limit is $7,500 (about $625 a month), plus a $1,100 catch-up from 50. Anything beyond those limits usually lands in a taxable brokerage account. See how much can I contribute to a 401(k) and how much can I contribute to a Roth IRA for the details.

Index funds answer where the money goes, not how much of it there is. The monthly amount still comes from the steps above. What index funds change is how easily a small, regular amount can be spread across hundreds of companies at low cost.

A common pattern is to put most of a monthly contribution into one or two broad funds, such as a total US market or S&P 500 fund plus an international fund, and to treat anything more specific as a smaller slice. Many brokers sell fractional shares, so a $100 monthly contribution can buy a slice of a fund whose single share costs several hundred dollars. What is an index fund explains how they work, and the index fund statistics page has cost and adoption figures.

Investing the same amount on the same day each month is called dollar-cost averaging. It buys more shares when prices are low and fewer when they are high, and it takes the timing decision out of each month. What is dollar-cost averaging and the dollar-cost averaging statistics cover how it compares with investing a lump sum.

Walnut does not move money from your bank. It reads your brokerage, helps you set a plan, and places trades at your broker only when you approve them. The steps below use features that exist in the product today.

1. Connect your brokerage

Link the account where your investments sit. Walnut reads your holdings and shows how the portfolio has done against the S&P 500. If you do not have an account yet, Public and Robinhood are two places to open one.

2. Set a goal

Add a goal with a target amount, a time horizon and a monthly contribution. Walnut projects whether your current balance and monthly investing are on track, so the abstract 15% becomes a number tied to something you care about.

3. Build a basket with target weights

A basket is a set of holdings with target weights, for example 70% in a broad US index fund and 30% in an international one. It gives each month's contribution a destination.

4. Add a recurring investment

A recurring investment spends a fixed amount across the basket's target weights on a schedule. It uses cash that is already in your brokerage account, so the transfer from your bank is set up at the broker or done by you. If the cash is not there on the day, the run is skipped and you are told.

5. Ask the assistant

The AI assistant can read your portfolio and your goal, and answer questions such as how your holdings have done against the S&P 500 or how far a basket has moved from its target weights.

Waiting for the perfect amount. Holding off until 15% is affordable often means investing nothing for years. Starting at a smaller figure and raising it by a point or two with each raise reaches the same place with less strain.

Leaving the employer match unclaimed. A match is part of pay that only arrives if you contribute. Contributing below the match threshold gives some of it back.

Investing money needed soon. A house fund invested in stocks can lose a quarter of its value the year before closing. Short-horizon money is commonly kept in cash or Treasury bills instead.

Stopping during a downturn. Pausing contributions when markets fall means buying fewer shares at lower prices, which is the opposite of what a monthly plan is designed to do.

Never revisiting the number. A figure set at a first job rarely fits ten years later. An annual check, often around a raise or tax time, keeps the monthly amount in step with income.

Personal saving rate: BEA, Personal Income and Outlays, August 2026. Household income and spending: BLS Consumer Expenditures, 2024. Savings guideline: Fidelity. Contribution limits: IRS, 2026 limits. Growth figures are Walnut's calculations from the stated assumptions and are illustrations, not predictions. Walnut is informational and is not an investment adviser. This guide is educational and not personalized financial advice.