結婚税計算ツール
The detailed guide below is currently available in English.
Where the marriage penalty and bonus come from
When two people file jointly, their incomes are stacked into one set of wider brackets and they claim one large standard deduction. If both partners earn similar amounts, that widening works in their favor and marriage produces a bonus. If one partner earns most of the money, the combined income may reach higher joint brackets faster than two separate returns would, producing a penalty.
What this comparison assumes
The "separately" scenario models two unmarried filers using single-style brackets (the closest match to married-filing-separately rules). Itemized deductions, tax credits, student-loan interest phaseouts, and state rules are all left out, so treat the result as a first look rather than filing advice.
よくある質問
Who usually gets a marriage bonus?
Couples with similar incomes — especially one earner with little or no income — typically pay less jointly than they would separately, because the joint brackets are twice as wide at lower incomes.
Does filing separately ever beat filing jointly?
Rarely. Separate returns get narrower brackets, but they can help in special cases such as separating large medical expenses or income-based student-loan payments. This calculator compares the extreme cases so you can see the size of the gap.