The most common reason people give for not investing is that they do not have enough money. The truth is that you can start investing with $100 a month — or even $25 — and build real wealth over time. The secret is not the amount; it is consistency, low costs, and starting early enough for compound growth to work. Here is a step-by-step plan for turning $100 a month into a serious investment portfolio, even if you have never bought a single share before.

Before you invest a dollar, make sure you have a small emergency cushion. You do not need a full six-month fund before you start — but you do need enough cash to handle a surprise car repair or medical bill without selling your investments at a loss. Aim for $500 to $1,000 in a high-yield savings account first, then start investing while you continue building the emergency fund. This order matters: investing without any cash buffer means the first emergency forces you to sell, often at the worst possible time. Think of the emergency fund as the foundation and investing as the house you build on top of it.

For most beginners, the best first account is a Roth IRA if you are eligible, because your money grows tax-free for decades. Open one at a low-cost brokerage like Fidelity, Vanguard, or Schwab — all of them allow you to start with no minimum deposit and charge no commission on stock and ETF trades. If your employer offers a 401(k) with a match, contribute enough to get the full match first, then open the Roth IRA with your $100 a month. If a Roth IRA does not fit your situation, a regular taxable brokerage account works fine too. The account you choose matters less than the habit of contributing every single month.

With $100 a month, simplicity wins. Buy a single low-cost total market index fund or ETF, such as a fund tracking the S&P 500 or the total US stock market. These funds own hundreds or thousands of companies at once, so you are diversified from day one, and their expense ratios are tiny — often 0.03 percent, which costs you just 3 cents a year per $100 invested. Avoid individual stocks at this stage: picking winners is hard, and one bad pick can wipe out months of contributions. Avoid expensive actively managed funds too. One broad index fund, bought every month, is the strategy that has beaten most professional investors over the long run.

Automation is what turns a good intention into a real habit. Set up an automatic transfer of $100 from your bank account to your brokerage on payday, and set up automatic investing so the money buys your index fund as soon as it arrives. When investing happens automatically, you never have to decide whether to invest this month — and you never have to resist the temptation to spend the money instead. Increase the amount whenever you get a raise: even $25 extra per month adds up to thousands over a decade. The best investment plan is the one that runs without willpower.

The numbers are encouraging. At an average 8 percent annual return, $100 a month grows to about $18,000 in 10 years, $59,000 in 20 years, and $150,000 in 30 years — and you will only have contributed $36,000 of that total. The rest is compound growth doing its work. At $200 a month, the 30-year figure is roughly $300,000. These are estimates, not guarantees, and the market will have bad years — but the pattern is clear: starting small and early beats starting big and late, because time matters more than the amount. The best day to start investing was ten years ago. The second-best day is today, with whatever you can afford.