A Marriage Bonus occurs when a couple pays less total income tax filing jointly as a married couple than they would have paid combined as two single filers. This most commonly happens when there is a significant income disparity between spouses (e.g., one primary earner and one stay-at-home or lower-earning spouse). The higher earner's income spills into the lower earner's unused lower tax brackets (10% and 12%), resulting in substantial tax savings.

A Marriage Penalty occurs when a married couple pays more combined tax filing jointly than if they had remained unmarried singles. It primarily affects couples where both partners earn similar high incomes (e.g. both earning $200k+), because the top 35% and 37% federal tax brackets for MFJ are not double the single brackets. Additionally, itemizing couples face a single $10,000 SALT cap jointly rather than two $10,000 caps as singles, and single parents lose the lower Head of Household rates.

Under current federal tax law, the State and Local Tax (SALT) deduction is capped at $10,000 per tax return. Two unmarried individuals living together can each deduct up to $10,000 ($20,000 combined). However, once married and filing jointly, they are limited to a single $10,000 cap, creating a direct $10,000 reduction in potential itemized write-offs for homeowners in high-tax states.

The Child Tax Credit ($2,000 per qualifying child under age 17) phases out starting at $200,000 Adjusted Gross Income (AGI) for single filers and $400,000 AGI for married couples filing jointly. Because the joint phaseout threshold is exactly double the single threshold, marriage does not trigger a Child Tax Credit penalty.

Married couples can choose "Married Filing Separately" (MFS). However, MFS rarely reduces the marriage penalty because many tax credits (such as the Earned Income Tax Credit and education credits) are disallowed, standard deductions and bracket limits are strictly halved, and if one spouse itemizes, the other spouse is forced to itemize (even if their deductions are $0).