No, it is not illegal to invest under 18. What’s actually going on is narrower and more practical: a minor cannot open a brokerage account or buy stocks, bonds, or funds in their own name, because people below the age of majority lack the legal capacity to enter binding contracts. The workaround is well established. An adult, usually a parent or grandparent, opens and manages an account on the minor’s behalf, and the young person gets the benefit of decades of compounding they’d otherwise miss.
Why a Minor Can’t Just Open a Brokerage Account
The barrier is contract law, not criminal law. A minor who signs an agreement can void it at any point before reaching the age of majority, and for a reasonable time afterward. Brokerages, banks, and mutual fund companies rely on enforceable contracts with their customers, so they won’t open accounts for someone who could walk away from the relationship at will. No statute makes it a crime for a 16-year-old to try to buy shares. The account application simply won’t go through.
That principle has been part of Anglo-American law for centuries, and it exists to protect young people from being locked into deals they don’t fully understand. The practical effect for a teenager who wants to invest is that an adult has to be involved.
Accounts an Adult Can Open for a Minor
There are three common structures, and the right one depends on where the money is coming from and what it’s meant to be used for.
Custodial Accounts (UGMA and UTMA)
The most common route is a custodial account under the Uniform Gifts to Minors Act (UGMA) or the Uniform Transfers to Minors Act (UTMA). An adult opens the account as custodian, chooses the investments, and manages the money until the child reaches the termination age set by state law. UTMA is available in every state except South Carolina, which uses UGMA only.
The main difference between them is what they can hold. UGMA accounts are limited to financial assets: cash, stocks, bonds, and mutual funds. UTMA accepts a broader range of property, including real estate, patents, and fine art, alongside all the financial instruments a UGMA can hold. For families buying stocks or index funds for a child, the distinction rarely matters.
Once you move assets in, they belong to the child irrevocably. You can’t take the money back, change your mind, or redirect it to a different beneficiary. The custodian has a fiduciary duty to manage the account for the child’s benefit, not for personal use. Earnings are reported under the child’s Social Security number.
Custodial Roth IRA
If the minor has earned income from a job or self-employment, a custodial Roth IRA is one of the most powerful tools available. Money goes in after tax, grows tax-free, and comes out tax-free in retirement. Opening one at 14 or 15 gives compound interest decades of extra runway that no amount of catching up later can match.
The contribution limit for 2026 is $7,500 or the child’s total earned income for the year, whichever is smaller. A teenager who earned $3,000 mowing lawns can contribute up to $3,000, not a penny more. The cash doesn’t have to come out of the child’s own bank account; a parent can fund the contribution as long as the child actually earned at least that much during the year.
What counts as earned income matters. Wages from a W-2 job qualify, and so does net self-employment income from babysitting, tutoring, freelance work, or a small lawn care business. Allowances, birthday money, and investment income do not. A parent or guardian manages the account until the child reaches the age of majority, at which point it becomes a standard Roth IRA in the child’s name. Contributions (but not earnings) can be withdrawn at any time without tax or penalty.
529 College Savings Plan
A 529 works differently from a custodial account in one important way: the account owner keeps control indefinitely. You can change the beneficiary to another family member, and the child never gains an automatic right to take over. For families worried about a young adult suddenly having unrestricted access to a large balance, that control matters.
Earnings in a 529 grow tax-free, and withdrawals are tax-free when used for qualified education expenses: tuition, room and board, books, and required supplies at eligible institutions. The tax-free treatment extends to K-12 tuition up to $10,000 per year and up to $10,000 lifetime for student loan repayment. Withdrawals for anything else trigger income tax on the earnings portion plus a 10% penalty.
Unused 529 funds can also be rolled into a Roth IRA for the beneficiary under rules added by the SECURE 2.0 Act, subject to a 15-year account age requirement, the annual Roth contribution limit, and a $35,000 lifetime cap per beneficiary.
What Happens When the Child Reaches the Termination Age
This is the single most important thing to understand before funding a custodial account. The termination age varies by state. Most states default to 21. A number allow termination as early as 18, and a few permit extensions to 25 or older. When the child hits that age, the custodian must hand over the assets. No conditions. No strings.
The now-adult beneficiary can spend the money on anything: college tuition, a car, a trip, or something you’d rather not think about. There is no mechanism to delay the transfer or hold back a portion of the funds. For a custodial Roth IRA, the account converts to a standard individual Roth IRA (some brokerages require opening a new account and transferring the assets rather than doing it automatically). For a UGMA or UTMA, the brokerage retitles the account in the beneficiary’s name alone.
If that possibility concerns you, and for large balances it probably should, a 529 or a formal trust gives the adult more lasting control. A trust is more expensive to set up but allows specific conditions such as reaching 25 or graduating college.
Taxes on a Minor’s Investment Income
Any investment held in a child’s name generates taxable income subject to the “kiddie tax.” For 2026, the first $1,350 of a child’s unearned income (interest, dividends, capital gains) is tax-free. The next $1,350 is taxed at the child’s own rate, typically 10%. Anything above $2,700 is taxed at the parent’s marginal rate, which can be substantially higher. The rule exists specifically to prevent parents from parking investment income in a child’s name to take advantage of lower brackets.
The kiddie tax doesn’t end at 18. It applies to children under 18, to 18-year-olds whose earned income doesn’t cover more than half their own support, and to full-time students aged 19 through 23 whose earned income doesn’t cover more than half their support. A college junior with a large custodial account and a part-time campus job is almost certainly still subject to it.
Emancipated Minors
A minor who has been legally emancipated, through a court order, marriage, or military service depending on the state, gains many of the legal rights of adults, including the capacity to enter contracts. In practice, most brokerages still require account holders to be 18, and some states keep restrictions on certain contracts even for emancipated minors. If this applies to you, contact the brokerage directly and expect to provide a copy of the emancipation order. The standard online application is unlikely to work.