Tax filing choices for the household under separable spheres bargaining

If household choices can be rationalized by the maximization of a well defined utility function, allowing spouses to file individually or jointly is equivalent to offering the envelope of the two tax schedules. If, instead, household ’preferences’ are constantly being redefined through bargaining, the option to file separately may affect outcomes even if it is never chosen. We use Lundberg and Pollak’s (1993) separate spheres bargaining model to assess the impact of filing options on the outcomes of primary and secondary earners. Threat points of the household’s bargain are given for each spouse by the utility that he or she attains as a follower of a counter-factual off-equilibrium Stackelberg game played by the couple. For a benchmark tax system which treats a couple’s average taxable income as if it were that of a single individual, we prove that if choices are not at kinks, allowing couples to choose whether to file jointly or individually usually benefits the secondary earner. In our numeric exercises this is also the case when choices are at kinks as well. These findings are, however, quite sensitive to the details of the tax system, as made evident by the examination of an alternative tax system.

Taxation of couples: a mirrleesian approach for non-unitary households

Optimal tax theory in the Mirrlees’ (1971) tradition implicitly relies on the assumption that all agents are single or that couples may be treated as individuals, despite accumulating evidence against this view of household behavior. We consider an economy where agents may either be single or married, in which case choices result from Nash bargaining between spouses. In such an environment, tax schedules must play the double role of: i) defining households’ objective functions through their impact on threat points, and; ii) inducing the desired allocations as optimal choices for households given these objectives. We find that the taxation principle, which asserts that there is no loss in relying on tax schedules is not valid here: there are constrained efficient allocations which cannot be implemented via taxes. More sophisticated mechanisms expand the set of implementable allocations by: i) aligning the households’ and planner’s objectives; ii) manipulating taxable income elasticities, and; iii) freeing the design of singles’ tax schedules from its consequences on households’ objectives.