Several parameters of the tax code change every year with the price of goods and services, as measured by the consumer price index for all urban consumers (CPI-U). Among the tax parameters that change are the amounts of personal and dependent exemptions; the size of the standard deductions; the income thresholds that divide the rate brackets for the individual income tax; the amount of annual gifts exempt from the gift tax; and the thresholds and phaseout boundaries for the earned income tax credit, the child tax credit, and several other credits. Indexing is intended to keep those amounts relatively stable in real (inflation-adjusted) terms.
Indexing is accomplished by adjusting each parameter from its value in a base year by the percentage change in the CPI-U between that base year and the most recent year for which information is available. The period used for the calculation is not a calendar year but the 12 months that elapse from September to August. The value of the CPI-U in August becomes available in September, which allows enough time to index the tax parameters and prepare the necessary forms for the coming year. Adjustments in parameters of the tax code are calculated as follows: In the base year of 1987, for example, the standard deduction for a single tax filer was $3,000. Between 1987 and 2010, the CPI-U increased by 93.9 percent; correspondingly, the standard deduction (rounded to the lowest $50 increment) increased to $5,800 for 2011.
The standard CPI-U, however, overstates changes in the cost of living by not fully accounting for the extent to which households substitute one product for another when the relative prices of products change. The Bureau of Labor Statistics created the chained CPI-U to explicitly address that "substitution bias" in the standard CPI-U. Whereas the standard CPI-U uses a basket of products reflecting consumption patterns that are as much as two years old, the chained CPI-U incorporates adjustments that people make in the types of products they buy from one month to the next. Although the chained CPI-U corrects for the substitution bias in the standard CPI-U, neither the chained nor the standard CPI-U perfectly captures changes in the cost of living because neither fully accounts for increases in the quality of existing products or the value of new products.
This option would use the chained CPI-U instead of the standard CPI-U to adjust various parameters of the tax code. The Congressional Budget Office estimates that the chained CPI-U is likely to grow at an average annual rate that is 0.25 percentage points less than the standard CPI-U over the next decade. Therefore, using the chained CPI-U to index tax parameters would increase the amount of income subject to taxation and result in higher tax revenues. Furthermore, the effects of instituting such a policy would grow over time. The net revenue increase would be about $700 million in 2012 but would reach $14 billion in 2021. Net additional revenues would total $17 billion over the 2012-2016 period and would sum to $72 billion from 2012 through 2021.
An argument in favor of using the chained CPI-U to index tax parameters is that this approach would more accurately adjust people's tax liability to reflect changes in the cost of living than the standard CPI-U. The chained CPI-U provides a better measure of changes in the cost of living by more quickly capturing the extent to which households adjust their consumption in response to changes in relative prices.
An argument against implementing this option is that only an initial estimate of the chained CPI-U is available on a monthly basis; a final and more accurate estimate is delayed because it is more complicated and time- consuming to compute the chained CPI-U than it is to compute the standard index. (The Congressional Budget Office discussed the details of this approach in a Web- only technical appendix released with its February 2010 issue brief Using a Different Measure of Inflation for Indexing Federal Programs and the Tax Code.) At the start of every year, all of the initial estimates for the prior year are revised, and one year later those interim estimates are further revised and made final. Because of those delays, the initial and interim estimates of the chained CPI-U, which typically contain errors, would need to be used to index the parameters in the tax code. Since the chained CPI-U was first published in 2002, however, the changes between the initial and final values have been relatively small. If the adjustment for each year was based on the index value from an earlier base year, those small errors would not accumulate beyond the current year. Furthermore, because the initial and interim estimates of the chained CPI-U have been closer to the final version of the chained CPI-U than the existing CPI-U has been, those estimates still reflect the basic improvement attributable to the chained CPI-U.