# Reference — US Personal Tax Return Preparation (Form 1040) All dollar figures are **tax year 2026** unless noted — verify at [irs.gov](https://www.irs.gov) before use. ## Contents - Schedule and form map - Common income documents - Standard vs itemized decision - Credit table with phase-out notes - Deadline calendar - Penalty structure - Worked mini-examples - Gotchas ## Schedule and form map | Situation | Where it goes | |---|---| | Wages (W-2) | 1040 line 1 | | Interest / ordinary dividends | Schedule B (if > $1,500), else 1040 directly | | Self-employment / gig income (1099-NEC, 1099-K) | Schedule C → SE tax on Schedule SE → Schedule 2 | | Capital gains, crypto/stock sales (1099-B) | Form 8949 → Schedule D | | Rental income, royalties, K-1 pass-through | Schedule E | | Adjustments (student loan interest, HSA, IRA deduction, ½ SE tax) | Schedule 1 Part II | | Other income (unemployment 1099-G, prizes, hobby) | Schedule 1 Part I | | Additional taxes (SE tax, early-withdrawal penalty, NIIT, AMT) | Schedule 2 | | Nonrefundable/refundable credits beyond CTC/EITC | Schedule 3 | | Itemized deductions | Schedule A | | Premium Tax Credit reconciliation (1095-A) | Form 8962 | | Retirement distributions (1099-R) | 1040 lines 4–5; Form 5329 if early | ## Common income documents - **W-2** — wages; one per employer; box 12 codes matter (D = 401(k), W = HSA employer contribution). - **1099-NEC** — contractor income ≥ $600 → Schedule C, even without the form. - **1099-INT / 1099-DIV** — interest/dividends; qualified dividends get capital-gains rates. - **1099-B** — broker sales; check basis was reported; reconcile on Form 8949. - **1099-R** — retirement distributions; code in box 7 drives taxability and penalty. - **1099-K** — payment platforms; report gross then back out personal/nontaxable items on Schedule 1. - **SSA-1099** — up to 85% of Social Security may be taxable depending on combined income. ## Standard vs itemized decision Itemize on Schedule A only if the sum beats the standard deduction ($16,100 single / $32,200 MFJ): - State and local taxes (SALT) — capped; verify the current cap for the tax year. - Home mortgage interest (1098) — acquisition-debt limits apply. - Medical expenses — only the portion above 7.5% of AGI. - Charitable donations — cash and fair-market-value of goods; receipts required at $250+. Rule: compute both, take the larger, and record the comparison so the choice is auditable. ## Credit table | Credit | Type | Key conditions | |---|---|---| | Child Tax Credit | Partially refundable | Qualifying child under 17 with SSN; phases out at higher AGI | | EITC | Refundable | Earned income + AGI limits by family size; investment-income cap; frequent audit target — document eligibility | | AOTC (education) | Partially refundable | First 4 years post-secondary, per student, needs 1098-T | | Lifetime Learning | Nonrefundable | Any post-secondary; per return | | Child & Dependent Care | Nonrefundable | Care enabling work; needs provider EIN/SSN | | Saver's Credit | Nonrefundable | Retirement contributions at lower AGI | | Premium Tax Credit | Refundable | Marketplace coverage; reconcile with Form 8962 — mandatory | Verify every phase-out threshold for the tax year at irs.gov; do not quote from memory. ## Deadline calendar (for tax year 2026) | Date | Event | |---|---| | Jan 15, 2027 | Q4 2026 estimated payment | | Jan 31, 2027 | W-2s and most 1099s due to recipients | | Apr 15, 2027 | Filing + payment deadline; Q1 2027 estimate; IRA/HSA contribution deadline for 2026 | | Jun 15, 2027 | Q2 estimate; automatic 2-month filing extension for taxpayers abroad (interest still runs) | | Sep 15, 2027 | Q3 estimate | | Oct 15, 2027 | Extended filing deadline (Form 4868 filed by Apr 15) | ## Penalty structure - **Failure to file:** 5% of unpaid tax per month, max 25%. Minimum penalty applies after 60 days. - **Failure to pay:** 0.5% per month, max 25%; drops to 0.25% under an installment agreement. - Both apply → file penalty is reduced by pay penalty for the overlap; filing on time is always worth it. - **Estimated-tax underpayment:** interest-based (Form 2210); avoided via safe harbor (90% current / 100% prior / 110% if prior AGI > $150k) or owing < $1,000. ## Worked mini-examples **Example 1 — standard vs itemized.** Single filer: SALT $9,000 (under cap), mortgage interest $5,500, donations $1,200 → itemized $15,700 < standard $16,100 → take standard. **Example 2 — safe harbor.** 2025 total tax $18,000, AGI $120,000; 2026 income jumps. Paying 100% × $18,000 = $18,000 through withholding/estimates avoids the underpayment penalty regardless of the 2026 bill. **Example 3 — gig worker.** 1099-NEC $22,000, expenses $4,000 → Schedule C net $18,000 → SE tax ≈ 15.3% × (18,000 × 0.9235) on Schedule SE; half of SE tax deducts on Schedule 1. ## Gotchas - An extension extends **filing only** — estimate and pay by April 15 or penalties/interest run. - 1099-K gross ≠ income: refunds, personal transfers, and basis must be adjusted, not ignored. - Dependents with jobs: they file their own return but must check "can be claimed as a dependent" — double-claiming causes e-file rejects. - Backdoor/IRA basis: Form 8606 must be filed every year with nondeductible contributions or basis is lost. - MFS traps: loses EITC, education credits, and usually the child-care credit; both spouses must match standard/itemized choice. - The IRS already has your W-2s/1099s — mismatches trigger automated CP2000 notices; reconcile every document, even small ones.