End-to-end workflow for a full-year Wisconsin resident sole proprietor or single-member LLC owner: compute federal Schedule C net profit, federal SE tax, federal Form 1040, then carry federal AGI into Wisconsin Form 1 with Schedule AD/SB additions and subtractions, apply the sliding-scale standard deduction, and calculate estimated-tax obligations on Form 1-ES.
Confirm the client is a full-year Wisconsin resident domiciled in Wisconsin and that the engagement is within scope (Form 1 — not Form 1NPR for part-year or nonresidents). Collect business information, entity type, and prior-year return to establish a baseline. Flag any bonus-depreciation or multi-state situations that require extra tracking.
Gather all business revenue, cost of goods sold, and deductible expenses to complete federal Schedule C. Identify home-office, vehicle, and depreciation deductions. Because Wisconsin does not conform to federal bonus depreciation (§168(k)), maintain a parallel Wisconsin depreciation schedule (Schedule AD add-back) for any listed or bonus-depreciation assets.
Compute self-employment tax on Schedule SE (net earnings × 92.35% × 15.3%, with the Social Security wage base cap applied). Determine all above-the-line deductions that reduce federal AGI — the 50% SE tax deduction, self-employed health insurance deduction, and any SEP-IRA, SIMPLE IRA, or solo 401(k) contributions. These reductions flow automatically into Wisconsin Form 1 Line 1.
Assemble the complete federal Form 1040 through Line 11 (federal AGI). Apply the federal standard deduction or itemized deductions and the §199A QBI deduction to arrive at federal taxable income and compute federal tax. Note that Wisconsin does NOT conform to §199A — the QBI deduction is irrelevant to the Wisconsin computation but the federal return must still be finalized before Wisconsin work begins.
Starting from federal AGI (Form 1040 Line 11 → Wisconsin Form 1 Line 1), calculate Wisconsin-specific additions on Schedule AD (primarily the §168(k) bonus-depreciation add-back, and any out-of-state income tax refunds deducted federally) and Wisconsin-specific subtractions on Schedule SB (U.S. government bond interest, qualifying retirement income if age 67+). The result is Wisconsin income on Form 1 Line 5.
Apply the Wisconsin sliding-scale standard deduction (maximum $14,260 single / $26,510 MFJ for 2025, phasing out at higher incomes) and personal exemptions ($700 per person) to arrive at Wisconsin taxable income on Form 1 Line 11. Apply the graduated rate schedule (3.50% / 4.40% / 5.30% / 7.65%) to compute Wisconsin tax. Identify applicable credits such as the Homestead Credit, the Earned Income Credit (Wisconsin version), the Working Families Tax Credit, or any credit for taxes paid to another state (Schedule OS).
Determine whether the client owes a penalty for underpayment of 2025 estimated tax (Wisconsin threshold: $500 expected liability). Project 2026 estimated tax payments using the current-year liability as a safe-harbor baseline. Prepare Form 1-ES vouchers for the four 2026 installment due dates (April 15, June 15, September 15, January 15). Confirm e-file readiness and review the final balance due or refund.
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