The Marriage Penalty and the Marriage Bonus
Marriage changes your tax bill before it changes anything else. Most thresholds in the code double for couples filing jointly — the tax brackets and the standard deduction (Table 6.1) among them — so for many couples filing jointly is a wash or a modest gain. The marriage bonus appears when a high earner marries a low or non-earner: the second spouse’s standard deduction and lower brackets absorb part of the first spouse’s income. Income that would have been taxed at 32–35% as a single filer drops into the 22–24% range. A stay-at-home spouse is, among other things, a tax shelter.
The marriage penalty appears when two high earners marry, because a handful of thresholds were never doubled. Consider two professionals, each with a $500,000 salary. As single filers, each has taxable income of after the 2026 standard deduction; the top 37% bracket begins at $640,600, so neither reaches it — their last dollars are taxed at 35%. Marry them and file jointly: the standard deduction does double, so combined taxable income is , but the 37% bracket for joint filers begins at $768,700 — not the $1,281,200 that doubling $640,600 would produce. Every bracket below the top is exactly twice its single-filer width, so the whole penalty is the two-point surcharge on the income squeezed above the joint threshold:
owed for nothing more than signing a marriage certificate.
The same non-doubling appears wherever Congress wrote one number where it should have written two, and two stacked high incomes collide with all of them at once:
- The SALT deduction cap — $40,400 for 2026 — is the identical dollar figure for a single filer and a couple, and so is the $505,000 of MAGI at which it starts phasing down toward the $10,000 floor. Two $300,000 earners are under the phase-out apart and well into it together.
- The NIIT (section “Net Investment Income Tax (NIIT)”) applies above $200,000 single against $250,000 joint ( IRC §1411(b), “Imposition of tax”), and the 0.9% Additional Medicare Tax uses the same pair ( IRC §3101(b)(2), “Rate of tax”). Neither threshold is indexed, so this penalty widens every year by construction.
- The $3,000 annual capital-loss deduction against ordinary income ( IRC §1211(b), “Limitation on capital losses”) is $3,000 for a couple as well — and $1,500 each if they file separately.
- The $750,000 acquisition-debt ceiling on the mortgage interest deduction ( IRC §163(h)(3), “Interest”) does not double either, so two people who each financed a house before the wedding find their combined deductible debt capped at one person’s limit.
Filing separately rarely cures the penalty — the married-filing-separately brackets are punitive and the status disables many credits (section “Filing status”). Reserve it for specific situations: shrinking a spouse’s income-driven student-loan payment, isolating yourself from liability for a spouse’s questionable return, or clearing an AGI-gated deduction threshold on one spouse’s lower income. The harshest version of the penalty is not on this list at all — it falls on a surviving spouse, whose brackets compress from joint to single overnight (section “The Widow’s Penalty”).
What the Joint Signature Actually Costs Understand what you sign, because the signature is the expensive part. A joint return creates joint and several liability: each spouse is independently liable for the entire tax, interest, and penalties, regardless of who earned the income, who prepared the return, or who lied on it. Divorce does not release you — a decree assigning the tax bill to your ex binds your ex, not the IRS, which will collect from whichever of you is easier to find. The exits are narrow and all live in IRC §6015, “Relief from joint and several liability on joint return”: innocent-spouse relief under IRC §6015(b) for an understatement you neither knew nor had reason to know about; separation of liability under IRC §6015(c), available once you are divorced, widowed, legally separated, or living apart for twelve months, which reallocates the deficiency along the lines of who generated it; and equitable relief under IRC §6015(f) for everything else, including tax that was correctly reported and simply never paid. The claim goes on Form 8857, “Request for Innocent Spouse Relief”. A spouse in a community-property state who files separately has a parallel remedy under IRC §66, “Treatment of community income”. If you have genuine doubts about what is on your spouse’s Schedule C, the higher tax of filing separately is the premium on an insurance policy against being liable for it.