What Generally Happens to Investing Gains in a Child's Account Tax-Wise?
An account gets opened for a child, birthday money and small contributions build up over the years, and eventually those funds start earning dividends or capital gains. At some point a parent files taxes and wonders whether any of that growth belongs on their own return, the child’s, or somewhere in between.
The short answer
Investment gains inside a custodial account generally belong to the child for tax purposes, since the account itself is legally the child’s property once funded. However, a set of rules often referred to informally as the “kiddie tax” can cause a portion of a child’s unearned income — including investment gains — to be taxed at the parent’s marginal rate above certain thresholds, rather than at the child’s typically lower rate.
Why gains don’t simply get the child’s low tax rate
- The kiddie tax rules exist to limit income shifting. Without some limit, families could move investment assets into a child’s name specifically to have the growth taxed at a lower rate, so these rules cap how much of a child’s unearned income gets favorable treatment.
- A portion is often tax-free, and a portion is taxed at the child’s rate. Amounts above those two tiers can be taxed using rates tied to the parent’s return, depending on how the specific thresholds and calculations apply that year.
- “Unearned income” is the key category. These rules generally apply to investment-type income — dividends, interest, capital gains — rather than money the child earns from a job, which is typically taxed under ordinary rules for the child’s own earned income.
- A separate return may be required. Depending on how much investment income a custodial account generates, a child may need their own tax return filed, or in some cases the income can be reported on a parent’s return instead, depending on the amounts involved.
How this differs from a 529 plan’s tax treatment
Custodial account gains and 529 plan growth are taxed under different frameworks entirely. Qualified withdrawals from an education-specific account can avoid tax on growth when used for qualifying expenses, which is a different structure than a custodial account’s blend of tax-free, child-rate, and parent-rate treatment. Families comparing the two often also look at how a 529 plan’s underlying investment options are typically structured since the investment menu and the tax treatment are both part of the comparison.
Why the numbers change year to year
The specific dollar thresholds that determine how much of a child’s investment income is tax-free, taxed at the child’s rate, versus taxed at the parent’s rate are set by the IRS and adjusted periodically, so they shift from year to year. Because of that, it’s more useful to understand the general three-tier structure than to memorize a specific figure, since whatever number applies in a given year may not hold the following year.
What families weigh once they understand this
Some families decide the simplicity of a custodial account is worth the more complex tax treatment, especially for smaller balances where the kiddie tax rarely comes into play in a meaningful way. Others lean toward education-specific accounts partly because of the different tax structure, on top of considerations like being able to change the account’s beneficiary to a different child later, which a custodial account doesn’t allow.
Where this leaves you
Investment gains in a custodial account are generally the child’s income for tax purposes, but the kiddie tax rules mean a meaningful chunk of that income can still end up taxed at a parent’s rate once it crosses certain thresholds. Understanding that three-tier structure matters more than any single number, since the specific dollar amounts are adjusted periodically rather than fixed.