Key figures
Wisconsin accounting
2026, with sources
A franchise tax measured by income
Wisconsin taxes corporations doing business in the state through a franchise tax measured by net income, at 7.9%. Most multistate businesses apportion income by the sales factor alone, and a unitary group must file a combined return (Form 6). The return is due on the 15th day of the 4th month after year end, the same as the federal return, and a federal extension automatically extends Wisconsin to 30 days after the federal extended date.
Corporations with at least $4 million of gross receipts also pay the economic development surcharge: the greater of $25 or 3% of Wisconsin gross tax liability, up to $9,800. For a startup it is a future line item, but it is a separate calculation that belongs in the provision once revenue gets there.
Where Wisconsin parts from the federal return
Wisconsin adopts the Internal Revenue Code as defined in its own statutes rather than as it changes, and it does not allow bonus depreciation. The federal bonus deduction is added back, assets are depreciated under regular rules, and Section 179 expensing is recomputed under the Code in effect for Wisconsin — which can produce a Wisconsin Section 179 deduction different from the federal one, prepared on a pro forma federal return.
Each federal change has to be checked against Wisconsin’s conformity statute before it is assumed to apply on the Wisconsin return.
What this means for the books
Take a Madison hardware-and-software startup that buys $400,000 of lab equipment and takes 100% bonus depreciation federally. For Wisconsin the bonus is added back and the equipment is depreciated over its MACRS life (or partly expensed under Wisconsin’s own Section 179), so Wisconsin taxable income is higher in year one and lower later. That is a Wisconsin-only temporary difference with its own deferred tax, and the fixed asset register needs a Wisconsin basis column.
Deadlines
- 15th day of the 4th month after year end — Apr 15Franchise or income tax return (Form 6 for combined groups)Form 4 / Form 6
- Mid-November (calendar year)Extended due date: 30 days after the federal extended due date
The federal baseline
This page covers what Wisconsin adds. The federal rules underneath it apply here too.
Common questions
Is Wisconsin’s “franchise tax” a second tax?
It is Wisconsin’s corporate income tax under another name. Corporations doing business in Wisconsin pay a franchise tax measured by net income, at 7.9%; an income tax at the same rate applies to a few foreign corporations not subject to the franchise tax. There is no separate capital-based franchise tax on top.
Can we take bonus depreciation in Wisconsin?
Wisconsin does not allow federal bonus depreciation; it is added back to federal taxable income and the asset is depreciated under regular rules. Wisconsin does allow a Section 179 deduction, computed under the Code as Wisconsin has adopted it, and it can differ from the federal election.
Accounting next door
- ILIllinois accountingIllinois taxes a C corporation’s income at 7% plus a 2.5% replacement tax, apportioned by a single sales factor and filed as a combined unitary group.
- IAIowa accountingIowa taxes corporations at 5.5% on the first $100,000 and 7.1% above for 2026, apportions by a single sales factor, and follows the federal code on a rolling basis.
- MIMichigan accountingMichigan taxes C-corps at 6% on a single sales factor once Michigan receipts reach $350,000, and decoupled from the federal R&D expensing change, so research costs are still amortized over five years for Michigan.
- MNMinnesota accountingMinnesota taxes corporations at 9.8% on a single sales factor, charges a minimum fee based on Minnesota property, payroll and sales, adds back 80% of bonus depreciation and caps NOL use at 70%.
Founder guides on this
- US GAAPUS GAAP for early-stage startups, in plain EnglishAccrual accounting, revenue recognition (ASC 606), leases (ASC 842), stock compensation and capitalized software: what each means for a small company.
- FundraisingAudit-ready books before your Series AInvestors, lenders and auditors ask for the same things: accrual statements, reconciled accounts and support for every balance. How to be ready first.
- R&D taxThe R&D tax credit and Section 174A for startupsEngineering salaries can earn a federal R&D credit against payroll tax, and Section 174A lets you deduct US research again. What qualifies, what to track.
More of the Wisconsin guide
- ReceivablesReceivables and sales tax in WisconsinSales tax registration, economic nexus, whether SaaS is taxable, and collecting from customers
- PayablesPayables and contractors in WisconsinPaying vendors and contractors: 1099 filing, use tax, contractor tests and withholding
- PayrollPayroll taxes and employer rules in WisconsinWithholding, unemployment insurance, paid leave, minimum wage and the rules on paydays
- ComplianceCompliance and filings in WisconsinRegistering to do business, annual reports, franchise tax and the filing calendar
- AdvisoryAdvisory: credits and decisions in WisconsinCredits, incentives and the decisions that are cheaper to get right the first time
Sources
Checked against each agency’s own page on . Rates and thresholds change, usually on January 1.
General information for US companies, not tax, legal or accounting advice for yours. Rules and thresholds change; confirm the specifics with a CPA or the agency before you act on them.