Form 1040 — U.S. Individual Income Tax Return: Complete Practitioner Guide to Every Line, Schedule, and Planning Opportunity for Tax Year 2026

The QBI deduction under IRC §199A (made permanent by the One Big Beautiful Bill) allows taxpayers with qualified business income from pass-through entities and self-employment to deduct up to 20% of their QBI. For taxpayers with taxable income below the threshold ($197,300 single / $394,600 MFJ for 2026), the deduction is simply 20% of QBI with no W-2 wage limitation. For taxpayers above the threshold, the deduction is limited to the lesser of 20% of QBI or 50% of W-2 wages paid by the business (or 25% of W-2 wages plus 2.5% of the unadjusted basis of qualified property). A client with both W-2 income and self-employment income calculates the QBI deduction based only on the self-employment income — the W-2 income from their employer is not QBI. The W-2 wages paid by the self-employment business (if any) are used in the wage limitation calculation. For a sole proprietor with no employees, the W-2 wage limitation can significantly reduce the QBI deduction above the threshold, which is one of the primary reasons practitioners recommend the S-corp election for high-income self-employed individuals — the S-corp pays W-2 wages to the owner, which satisfies the wage limitation and preserves the full QBI deduction.

For a client who is just over a bracket threshold, the goal is to reduce taxable income below the threshold to move a portion of income into the lower bracket. The most effective strategies, in order of impact, are: (1) maximize pre-tax retirement contributions — 401(k) contributions ($24,500 in 2026, or $32,500 with catch-up for age 50+) directly reduce AGI and taxable income; (2) maximize HSA contributions ($4,400 self-only or $8,750 family in 2026) if the client has a qualifying high-deductible health plan; (3) defer income to the following year if the client has flexibility over the timing of self-employment income, bonuses, or year-end invoicing; (4) accelerate deductions into the current year — prepay deductible expenses, make charitable contributions, or bunch itemized deductions in the current year if the client alternates between standard and itemized deductions; (5) consider a defined benefit plan or cash balance plan if the client is self-employed and has significant income above the 401(k) limit. The bracket threshold analysis should be done in the context of the client’s full tax picture, including the impact on AGI-dependent phase-outs (IRA deductibility, EITC, child tax credit, SALT limitation).

Married filing separately (MFS) is almost always more expensive than married filing jointly (MFJ) because of the numerous penalties built into the tax code for MFS filers. MFS filers lose: (1) the student loan interest deduction; (2) the American Opportunity and Lifetime Learning Credits; (3) the Earned Income Tax Credit; (4) the Child and Dependent Care Credit; (5) the ability to contribute to a Roth IRA (the MFS Roth IRA phase-out begins at $0 of MAGI); (6) the $25,000 rental real estate allowance; and (7) the exclusion of Social Security benefits from income. Despite these disadvantages, MFS can be beneficial in specific situations: (1) when one spouse has very high medical expenses that exceed 7.5% of their individual AGI but not 7.5% of the combined AGI; (2) when one spouse has significant student loan debt on an income-driven repayment plan (MFS keeps the other spouse’s income out of the payment calculation); (3) when one spouse is concerned about liability for the other spouse’s tax debt or fraudulent return; or (4) in community property states where the income allocation rules create unusual results. Practitioners should always run a joint vs. separate comparison before recommending MFS.

The Net Investment Income Tax (NIIT) under IRC §1411 imposes an additional 3.8% tax on the lesser of (1) net investment income or (2) the excess of MAGI over the threshold amount ($200,000 for single filers, $250,000 for MFJ, $125,000 for MFS — these thresholds are not indexed for inflation). Net investment income includes: interest, dividends, capital gains, rental income (unless the taxpayer qualifies as a real estate professional), royalties, passive activity income, and income from trading in financial instruments. Net investment income does not include: wages, self-employment income, active business income, Social Security benefits, IRA distributions, 401(k) distributions, or tax-exempt interest. The NIIT is reported on Form 8960 and added to the regular tax on Schedule 2. For high-income clients, the NIIT effectively raises the top rate on investment income to 23.8% (20% capital gains rate + 3.8% NIIT) and the top rate on ordinary investment income to 40.8% (37% + 3.8%). The most effective strategies for reducing NIIT exposure are: converting passive rental income to non-passive income by qualifying as a real estate professional; investing in tax-exempt municipal bonds; maximizing retirement account contributions to reduce MAGI; and using tax-loss harvesting to reduce net capital gains.