Kiddie tax
The Kiddie tax rule can be found in the US tax code^{[1]} which "taxes certain unearned income of a child at the parent’s marginal rate, no matter whether the child can be claimed as a dependent on the parent’s return."^{[2]} The updates are in section A(1)(11001)(a)(4) of the 2018 tax law.^{[3]}
The kiddie tax in general
There are two rules that may affect the tax and reporting of the investment income of certain children:^{[4]}
 If the child's interest, dividends and other unearned income total more than $2,200 in 2020 or 2021 (twice the basic standard deduction for a dependent minor of $1,100, indexed for inflation^{[note 1]}), part of that income may be subject to tax at the rate for trusts (in 2018 and later) instead of the child's tax rate.
 If the child's interest and dividend income (including capital gain distributions) total less than $11,000 (10 times the basic standard deduction of $1,100), the child's parent may be able to elect to include that income on the parent's return rather than file a return for the child. This may result in paying more tax than having the child file a tax return, but given the high tax rates for trusts, it might also result in paying lower tax. (See Form 8814 and Publication 929).
The following characterizes the kiddie tax:
 Applies if the child is < 24 and a full time student (lower ages if not), and has > $2,200 in unearned income for 2020 or 2021
 Anything over $2,200 in unearned income is taxed at the tax rate for the parents
 Kiddie tax is calculated on Form 8615 and paid on child's return
 The standard deduction for a child who can be claimed as a dependent is the greater of
 $1,100 for 2020 or 2021 (indexed for inflation)
 earned income plus $350 for 2020 or 2021 (indexed for inflation) but not more than the regular standard deduction amount, generally $12,400 for 2020, $12,550 for 20201(indexed for inflation)
 Note that by gifting appreciated securities to a child, one can save at most $165 per year per child in capital gains tax in 2020 or 2021 (if in the 15% Long Term Capital Gains (LTCG) bracket) and rarely as much as $1064 per year per child (if in the 37% bracket with tax loss carryover, see note below)
Taxation of children with no earned income
If the children have no earned income then:
 The child (if a dependent) gets a Standard Deduction of $1,100
 This has the effect of:
 The first $1,100 of unearned income is untaxed
 The next $1,100 is taxed at the child's rate
 0% for qualified dividend (QDI) and long term capital gain (LTCG)
 10% for Interest and nonQDI
 Anything beyond that is taxed at the parents' tax rate
Taxation of children with earned income
If the children have earned income then:
 The standard deduction is $1,100 for 2020 or 2021, or (earned income + $350), whichever is larger, but not more than the normal standard deduction of $12,400 for 2020, $12,550 for 2021 (indexed for inflation) for a single person.
Examples:
Example 1: A child has $200 of earned income. His standard deduction is $1,100. With $500 of ordinary unearned income (interest, shortterm capital gains (STCG), and nonQDI) and $1,300 of tax advantaged unearned income (QDI and LTCG), his total income is $2,000, and his taxable income is $900. Under the "income stacking rules" of the Qualified Dividends and Capital Gain Tax worksheet, all of his taxable income is tax advantaged, and his tax is $0.
Example 2: A child has $1,200 of earned income. Her standard deduction is $1,550 ($1,200 + $350). With $500 of ordinary unearned income (interest, STCG, and nonQDI) and $1,300 of tax advantaged unearned income (QDI and LTCG) her total income is $3,000, and her taxable income is $1,450. Under the "income stacking rules" of the Qualified Dividends and Capital Gain Tax worksheet, the taxable income consists of $150 of ordinary income ($500  $350) and $1,300 of tax advantaged income. Her tax will be $15 (10% of $150).
Example 3: Your child has no other income than $3,000 of LTCG from stock you gave her. Her standard deduction is $1,100 and her taxable income is $1,900. In 2020, since her unearned income is over $2,200, the last $800 is taxed at the parents' rate; if the parents pay 15% tax on LTCG, the tax is $120.
Example 4: Your child has no other income than $1,000 of LTCG from stock you gave him. His standard deduction is $1,100 and his taxable income is zero. You save $150 (15% of $1,000) in the 15% LTCG bracket.
State kiddie tax
California has a kiddie tax which follows the federal rules ^{[5]}.
Notes
 ↑ The basic standard deduction is indexed for inflation. The unearned income limit is twice that amount. Source: 26 USC 63:(c)(4) and 26 USC 1:(g)(4)(A)
Tax loss carryover
If a parent is in the 37% marginal income tax bracket and already has a $3,000 tax loss carryover, then a longterm capital gain of $3,000 will be offset by that $3,000 loss and no tax will be due. However, the $3,000 tax loss carryover could have been used to offset ordinary income if it exceeds the parents' capital gains; that would save 37% of $3,000, which is $1,110. If this is the child's only income, $800 is subject to 20% tax, giving the child a $160 tax bill. You can save another $114 because the $3,000 capital loss reduces the income subject to the 3.8% Net Investment Income Tax, for a total savings of $1,064. Thus, gifting to a child may still make financial sense.
See also
References
 ↑ 26 U.S. Code § 1  Tax imposed  LII / Legal Information Institute, viewed January 24, 2015.
 ↑ Samuel Donaldson, Federal Income Taxation of Individuals: Cases, Problems and Materials 639 (Thomson West 2007) (2005).
 ↑ http://docs.house.gov/billsthisweek/20171218/CRPT115HRPT466.pdf
 ↑ Tax Topics  Topic 553 Tax on a Child's Investment Income (Kiddie Tax), viewed January 24, 2015.
 ↑ CA FTB Form 3800, retrieved January 17, 2021
External links
 Kiddie tax, on Wikipedia
 Understanding the Kiddie Tax, from Intuit
