In December 2010, the 2001-2003 tax cuts, which were set to expire after 2010, were extended for an additional two years ( P.L. 111-312 ). The American Recovery and Reinvestment Act of 2009 ( P.L. 111-5 ) contained temporary provisions that are aimed at middle-class and lower-income families. 112-1240 ) and made permanent at the end of 2015 by the Protecting Americans from Tax Hikes (PATH) Act ( P.L. 114-113 ). This shift of burden to families with children was changed dramatically by the adoption of the $500 child credits in the Taxpayer Relief Act of 1997 and by the increase in that credit to $1,000 in the Economic Growth and Tax Relief Reconciliation Act of 2001. These changes increased the marriage bonus. These provisions were extended on two occasions and were made permanent by the PATH Act ( P.L. These provisions benefit large low-income families and reduce the marriage penalty. For the income tax, this standard might mean that families of the same size with the same income should pay the same tax. Provisions included in the calculations are the rate structure, the most beneficial of standard deductions or itemized deductions (the latter are assumed to be 15% of income, with 5% of income reflecting state and local taxes included in the alternative minimum tax base), personal exemptions, the earned income credit, the child credit, and the alternative minimum tax. Table 2 reports the tax rates for higher-income families. Moreover, the variation across families that have the same ability to pay is substantial. The child credit also contributes to the favorable treatment of families with children, including in the middle and upper middle income levels where it is not phased out. The provisions that increase the phase-out level for the earned income credit reduce tax burdens for low-income joint returns and further reduce marriage penalties and increase marriage bonuses. At the lowest income level, and a 50/50 split, one of the singles files a single return with a very small negative rate because of the small earned income credit for those without children, while the other claims a child and has a much higher negative tax rate than a married couple because there is no phaseout of benefits. Conclusion

The analysis of equity across families suggests that, based on an ability-to-pay standard, families with children are paying lower rates of tax (or receiving larger negative tax rates) than single individuals and married couples at lower and middle incomes, while families with children are being taxed more heavily at higher-income levels. At the lowest income levels, the EIC plus child credits provide the largest tax subsidies to families with two to four children. The smallest subsidies go to childless couples or individuals. At middle-income levels, families with many children will have the most favorable treatment because of the effect of the child credit, which has a very large effect relative to tax liability. At higher-income levels, large families are penalized because the adjustments for children such as personal exemptions and child credits are too small or are phased out, while graduated rates cause larger families that need more income to maintain a given living standard to pay higher taxes. Tax rates are more variable at lower-income levels. At all but the lowest and highest income levels, singles pay higher taxes than married couples without children.
Individual income tax provisions have shifted over time, first in increasing the burden on larger families, and then in decreasing it. These shifts were caused by changing tax code features: personal exemptions, standard and itemized deductions, rates, the earned income credit (EIC), the child credit, and other standard structural aspects of the tax. Some of these features reflect changes made by the 2001 Bush tax cuts, which were extended for an additional two years by P.L. 111-312 and largely made permanent by the American Taxpayer Relief Act (P.L. 112-240). The most recent legislative change was making the temporary provisions liberalizing the child credit and earned income credit enacted in the American Recovery and Reinvestment Act of 2009 (P.L. 111-5), and subsequently extended, permanent. These provisions were made permanent at the end of 2015 by the Protecting Americans from Tax Hikes (PATH) Act (P.L. 114-113).
Taxes as a share of income have decreased for lower-income families and to a lesser extent for middle-income families, while remaining at approximately the same level for higher-income families.
While several standards may be considered in determining equitable treatment of families over family type and size, a standard approach is based on ability to pay, so that large families with the same income as small ones pay less tax. Based on this standard, the analysis of equity across families suggests that families with children are paying lower rates of tax (or receiving larger negative tax rates) than single individuals and married couples at lower and middle incomes. However, families with children are being taxed more heavily at higher-income levels. At the lowest income levels, the EIC provides the largest tax subsidies to families with three children. The smallest subsidies go to childless couples. At middle-income levels, families with many children will have the most favorable treatment, due to the effect of the child credit, which has a very large effect relative to tax liability. At higher-income levels, large families are penalized because the adjustments for children, such as personal exemptions and child credits, are too small or are phased out, while graduated rates cause larger families that need more income to maintain a given living standard to pay higher taxes. Tax rates are more variable at lower-income levels. At all but the lowest and highest income levels, singles pay higher taxes than married couples.
The analysis of the marriage penalty indicates that marriage penalties have largely been eliminated for those without children throughout the middle-income range, but this change has inevitably expanded marriage bonuses. Marriage penalties remain at the high and low income levels and could also apply to those with children, where the penalty or bonus is not very well defined. But by and large, the current system is likely to encourage rather than discourage marriage and favors married couples over singles.
The analysis of equity across families suggests that increases in earned income tax credits for those without children would lead to more equal treatment based on the ability to pay approach, while full refundability of the child credit would exacerbate inequalities. At the higher end of the scale, eliminating phase outs of provisions that differentiate across families would probably lead to more equitable treatment, and limiting or repealing the alternative minimum tax would reduce the burden of taxes on families with children at upper middle-income levels as well as marriage penalties.