At the first level, our federal income tax system is one of self-assessment. A taxpayer is required to report items of income, deduction, gain, and loss on a return and compute her taxable income and the tax thereon. The taxpayer must sign and file the return, and pay the amount of tax shown due. The IRS is authorized to review and challenge the self-assessed tax liability, and through administrative and judicial proceedings, the taxpayer may ultimately be found to be liable for a deficiency – the difference between the correct tax due and the amount of tax shown on the return. The deficiency may also include interest charges on taxes paid later than their due date and penalties for failure to self-assess and pay the correct amount of tax due.
A husband and wife who choose to file a joint federal income tax return engage in this self-assessment process jointly. The joint return aggregates items of income, deduction, gain, and loss attributable to either spouse; taxable income is computed in the aggregate, and the tax due is a single amount. If a joint return is made, each spouse undertakes to pay the entire amount of tax shown due. Furthermore, each spouse assumes joint and several liability for the entire amount of any subsequently determined deficiency.
From a collection standpoint, joint and several liability allows the IRS to collect from either spouse the full amount of any deficiency. If the IRS collects the entire amount of a deficiency from one spouse, that spouse has contribution rights against the other spouse for the portion of the deficiency attributable to the other spouse.