How to Start Investing With $100 a Month

By Alexander, Squared Roots · November 2, 2026 · 4 min read

A lot of people put off investing because they think they need thousands of dollars to start, or because it feels like something for people who already know what they're doing.

The truth is that for most people, wealth isn't built by picking the right stock. It's built by investing regularly, for a long time, in low-cost, diversified funds, and leaving it alone. $100 a month is a real start.

This article is general education, not personal investment advice. What's right for you depends on your full situation.

What $100 a month can become

Here's what regular monthly investing could grow to, assuming a steady 7% average annual return compounded monthly:

These are illustrations, not predictions. Real returns vary year to year, can be negative, and aren't guaranteed.

Notice what happens with $100 a month over 30 years: you put in $36,000, and growth does the rest. That's the power of time, and it's why starting small now often beats starting big later.

Before you invest: have these in place

Investing works best when you won't be forced to sell at a bad time. Before you put money in the market, try to have:

1. A starter emergency fund of at least $1,000. Otherwise, the next car repair might mean selling investments while they're down. (More on emergency funds.)
2. A plan for high-interest debt. If you're paying 20% or more on credit cards, paying that down is a guaranteed "return" that's hard for any investment to match.
3. Any employer match. This is the exception to the order above (see below).

Step 1: Get any employer match

If your employer offers a 401(k), 403(b) or similar plan with a match, that's often the best place to start. For example, an employer might match 50 cents for every dollar you contribute, up to a certain percentage of your pay.

That match is part of your compensation. Not contributing enough to get it is leaving money on the table. Check your benefits paperwork or ask HR:

• Is there a match?
• How much do I need to contribute to get all of it?
• When does the match "vest" (become fully yours)?

Step 2: Understand IRAs

An IRA (individual retirement account) is a retirement account you open yourself at a brokerage. There are two main types:

• Traditional IRA: contributions may be tax-deductible now; you pay taxes when you withdraw in retirement.
• Roth IRA: you contribute money you've already paid taxes on; qualified withdrawals in retirement are tax-free.

Both have annual contribution limits and some income rules, which change over time. Check IRS.gov for this year's numbers, or ask a tax professional which fits you.

Step 3: Choose simple, diversified, low-cost funds

You don't need to research individual companies. Many long-term investors use:

• Index funds, which hold many companies at once and aim to match a market index rather than beat it.
• Target-date funds, which pick a mix of investments for you based on the year you plan to retire, and gradually become more conservative as that year gets closer.

Whatever you look at, check the expense ratio, which is the yearly fee the fund charges as a percentage of your investment. Lower is better, and over decades, small differences in fees add up to big differences in what you keep.

Step 4: Automate it

Set up an automatic contribution, ideally right after payday. Automatic investing means:

• you don't have to remember
• you don't have to decide each month
• you buy regularly whether markets are up or down, which takes emotion out of it

Step 5: Increase it over time

Every time you get a raise, bump your contribution by 1% or more. Because it happens at the same time as the raise, you'll barely notice the difference in your paycheck, but your future self will.

Step 6: Leave it alone

Markets go down sometimes, occasionally a lot. If you're investing for something 10, 20 or 30 years away, short-term drops are normal. Selling during a downturn locks in the loss. The people who do best over time are often the ones who check their balances the least.

When to get help

If you have questions about which accounts or funds fit your situation, consider talking with a fee-only fiduciary financial adviser. "Fee-only" means they're paid by you, not by commissions on what they sell you. "Fiduciary" means they're required to act in your best interest.

The short version

1. Build a starter emergency fund and a plan for high-interest debt.
2. Get any employer match.
3. Learn the difference between traditional and Roth IRAs.
4. Use low-cost, diversified funds.
5. Automate your contributions.
6. Raise them with every raise.
7. Leave it alone and let time work.

Getting your budget, cushion and debt plan in place is the foundation that makes investing possible. The Squared Roots Money Toolkit helps you do exactly that. See what's inside.