The Widespread Prevalence of Marriage Penalties : Testimony Before the Subcommittee on the District of Columbia, Committee on Appropriations, United States Senate

Citizens pay an overall marriage penalty when their combined social welfare benefits less taxes are lower when they are a married couple than when they are two single individuals. Because marriage is optional, marriage penalties or subsidies are assessed primarily for taking wedding vows, not for living together with other adults (although there are some exceptions).