The Earned Income Tax Credit (EITC) is a refundable tax credit available to eligible low-wage workers. Many low-income workers, especially those with children, can receive several thousand dollars of financial assistance from this tax provision. (Childless recipients can receive slightly less than $500 if they qualify for the maximum credit.) Because the credit is refundable, an EITC recipient need not owe taxes to receive the benefit. In the 113 th Congress, many legislative proposals have been introduced that would modify the EITC. In general, these bills modify either how the credit is calculated or eligibility requirements for the credit, or both. To understand how these bills would modify the credit, this report first provides a brief overview of eligibility requirements for the credit and how the credit is calculated under current law. (For a more detailed description of EITC eligibility requirements and the calculation of the credit, see CRS Report RL31768, The Earned Income Tax Credit (EITC): An Overview , by [author name scrubbed].) The report then summarizes how different legislative proposals modify certain parameters of the credit, starting with modifications that expand the credit for workers without qualifying children , followed by those that expand the EITC for workers with qualifying children . (Some legislative proposals modify the credit for workers both with and without children.) O ther modifications to the credit, including those made by House Ways and Means Committee Chairman Camp 's tax reform proposal, are briefly summarized. Eligibility for and the amount of the EITC are based on a variety of factors, including residence and taxpayer ID requirements, the presence of qualifying children, age requirements for certain recipients, amount of investment income, and the recipient's earned income. This section briefly describes key eligibility factors and provides an overview of how eligible taxpayers calculate the value of the credit under current law. There are a variety of eligibility criteria for the EITC, described below. Residence and ID Requirements: Under current law, an EITC recipient must be a resident of the United States, unless the recipient resides in another country because of U.S. military service. In addition, to be eligible for the credit, the tax filer must provide valid Social Security numbers (SSNs) for work purposes for themselves, spouses if married filing jointly, and any qualifying children. Definition of Qualifying Child: To be considered a "qualifying child" of an EITC recipient, three requirements must be met. First, the child must have a specific relationship to the tax filer (son, daughter, step child or foster child, brother, sister, half-brother, half-sister, step brother, step sister, or descendent of such a relative). Second, the child must share a residence with the taxpayer for more than half the year in the United States. Third, the child must meet certain age requirements ; namely, the child must be under the age of 19 (or age 24, if a full-time student) or be permanently and totally disabled. Age Requirements for EITC Recipients with No Qualifying Children: If a tax filer has no qualifying children , he or she must be between 25 and 64 years of age. Childless taxpayers under age 25 or older than 64 are not eligible for the EITC. There is no age requirement for tax filers with qualifying children. Investment Income: Tax filers with investment income greater than $3,350 in 2014 are ineligible for the EITC. Investment income includes interest income (including tax-exempt interest), dividends, net rent, and royalties that are from sources other than the filer's ordinary business activity, net capital gains, and passive income. The EITC is calculated based on a recipient's earnings. Specifically, the EITC equals a fixed percentage (the "credit rate") of earned income until the credit amount reaches its maximum level. The EITC then remains at its maximum level over a subsequent range of earned income, between the "earned income amount" and the "phase-out amount." Finally, the credit gradually decreases in value to zero at a fixed rate (the "phase-out rate") for each additional dollar of earnings above the phase-out amount. The specific values of these EITC parameters (i.e., credit rate, earned income amount, etc.) vary depending on the several factors, including the number of qualifying children and the marital status of the tax filer, as illustrated in Table 1 . Figure 1 provides a graphic representation of the amount of the EITC for an unmarried EITC recipient with one child in 2014. As illustrated in Figure 1 (and in the "one qualifying child" column in Table 1 for unmarried tax filers), the credit phases in at a rate of 34% of earnings for tax filers with earnings under $9,720 in 2014. At $9,720 of earnings, the EITC reaches its maximum level of $3,305 and remains at that level until earnings exceed $17,830. For taxpayers with earnings above this threshold, the $3,305 amount is gradually reduced by 15.98 cents for every dollar above $17,830. Unmarried tax filers with one child and earnings at or above $38,511 are ineligible for the EITC. Several bills introduced in the 113 th Congress would expand the EITC for childless workers. These bills— H.R. 4117 , H.R. 2116 , S. 836 , S. 2162 , H.R. 2359 , and the Obama Administration's FY2015 budget—would modify how the credit is calculated, increasing the amount of the credit for childless workers. All of these bills—except H.R. 2359 —would also modify various eligibility rules for the credit, expanding the number of taxpayers eligible to claim it. These legislative changes are summarized below in Table 2 and described subsequently in this report. A variety of legislative changes made to the formula used to calculate the EITC for childless workers would increase the amount of the credit. Generally, these bills would increase a variety of different parameters, including the credit rate, the earned income amount, and the phase-out income level. As illustrated in Figure 2 and Figure 3 , these changes would generally increase the maximum value of the credit for childless workers from $496 to approximately $1,000 (Administration budget proposal); $1,300 ( H.R. 2359 ); $1,350 ( H.R. 2116 , S. 836 , S. 2162 ); or $1,500 ( H.R. 4117 ). Under current law, the credit rate for childless EITC recipients is 7.65%. All else being equal, increasing the credit rate would increase the amount of the credit. Under H.R. 4117 , the credit rate for childless workers would increase to 23.15% (the phase-out rate would also increase from 7.65% to 23.15%). Under H.R. 2359 , the credit rate for childless workers would increase to 20% (the phase-out rate would remain at its current level of 7.65%). Under H.R. 2116 , S. 836 , S. 2162 , and the FY2015 Administration budget proposal , the credit rate for childless workers would double to 15.3% (the phase-out rate would also increase from 7.65% to 15.3%). As previously discussed, the "earned income amount" is the earnings level at which the credit reaches it maximum value. All else being unchanged, increasing the earned income amount increases the amount of the credit for most EITC claimants. For example, under current law, the earned income amount for a childless EITC claimant is $6,480. If the earned income amount was increased to $10,000 (and all other parameters of the credit remained unchanged from current law), all tax filers with income above the current earned income threshold of $6,480 would receive a larger credit. The maximum value of the credit would increase from $496 to $765. Under H.R. 2116 , the earnings level at which the childless EITC reaches its maximum value would increase from its current level of $6,480 to $8,820 (adjusted annually for inflation). The EITC phases out for recipients when income exceeds a "phase-out amount." Increasing the phase-out amount increases the credit amount for tax filers whose income places them in the downward sloping "phase-out range" of the credit (see Figure 1 for an illustration of the "phase-out range"). Under current law, the phase-out amount for unmarried tax filers is specified by law and the phase-out amount for married tax filers is calculated by adding the applicable amount of marriage penalty relief. (For example, as illustrated in Table 1 , the phase-out amount for married taxpayers with a given number of children is calculated by adding $5,430—the current level of "marriage penalty relief"—to the phase-out amount for unmarried recipients with the same number of children.) Beginning in 2018, this marriage penalty relief is scheduled to revert permanently to $3,000 (adjusted for inflation). H.R. 4117 would increase both the phase-out amount and marriage penalty relief. Specifically, the bill would increase the phase-out amount from its current level of $8,110 for unmarried tax filers to $16,630 (and subsequently adjust this amount for inflation in future years). For childless workers only, this bill would also increase marriage penalty relief permanently to $8,000 (adjusted for inflation). H.R. 2116 would increase the phase-out amount for unmarried recipients to $10,425 (and adjust this amount annually for inflation). The 2009 temporary increase in the marriage penalty relief of $5,000 (adjusted for inflation, $5,430 in 2014) would also be made permanent.