FormU: FormU (2025)
Wisconsin · Wisconsin DOR · Used for tax years 2025
Wisconsin Form U calculates a corporation’s underpayment of estimated tax and the interest due for 2025. It also includes calculations for amounts due on returns filed after the unextended due date and a worksheet for the annualized income installment method. It is filed with Wis
Who files this form
Wisconsin Form U is for corporations calculating underpayment of estimated tax and related interest. The 2025 form says to file it with Wisconsin Form 4, 4T, 5S, or 6.
Complete Part II only if your return is filed after the unextended due date and shows tax due. Complete Part III only if you use the annualized income installment method to calculate required installments.
When it's due
For tax year 2025, Part II, line 21 identifies the amount due on the 15th day of the 3rd or 4th month after the end of the taxable year. The form does not explain which month applies to each filer.
The form refers to instructions for installment due dates, but those instructions are not provided here. No specific calendar filing date is printed in the supplied form text.
What you'll need
Have the following information available to complete the form:
- Corporation or designated agent name and federal employer ID number.
- 2025 net tax, economic development surcharge, refundable credits, and Wisconsin tax withheld.
- 2024 net tax, economic development surcharge if applicable, and refundable credits for the prior-year comparison.
- Estimated tax and surcharge payments, including payment dates, overpayments, and late payments.
- Your return's filing date, extension status, and balance-due payment date, as applicable.
If using Part III, you also need Wisconsin net income for each annualization period, adjustments, nonrefundable credits, refundable credits, and the economic development surcharge.
How to file
File Form U with Wisconsin Form 4, 4T, 5S, or 6. The supplied form does not give a mailing address or e-filing directions.
Enter the Part I, line 17 interest total on the line provided on your tax return, unless the return is filed after the unextended due date and shows tax due. In that case, carry the total to Part II, line 22.
If completing Part II, enter the line 26 total on the line provided on your return and increase the “Amount Due.”
Common mistakes
- Including estimated payments in refundable credits. Lines 1b, 3b, and 37 specifically exclude estimated tax and surcharge paid.
- Continuing line 2 when line 1e is zero. If the amount calculated for line 1e is less than $500, enter $0 and go to Part II if applicable. Do not complete line 2 when line 1e is $0.
- Dividing by four for a short tax year. Lines 6 and 43 direct you to divide by four only for a 12-month tax year. For a shorter year, they refer you to the instructions.
- Completing Part III across rows instead of by column. Finish one column through line 47 before starting the next column.
- Applying Part II payments to the wrong column first. Line 20 says to apply payments first to the 18%-per-year column.
Questions people ask
What interest rate applies to estimated tax underpayments in Part I?
Lines 15 and 16 use 12% per year, based on the amounts and number of days entered on the form.
When can I use the prior-year tax comparison on line 4?
If 2025 net income is less than $250,000 and the 2024 return covered 12 months, line 4 says to enter the smaller of line 2 or line 3c. Otherwise, enter line 2. Tax-option (S) corporations making the entity-level tax election are directed to the instructions.
How do I use the annualized income installment method?
Complete Part III first. Carry the amounts from line 47 to Part I, line 6. The form refers to instructions for the annualization periods and other worksheet details.
What late-filing charges does Part II list?
If the return is filed late without an extension or after the extended due date, line 25 lists a penalty of 5% of net tax due for each month or fraction of a month the return is late, up to 25%, plus a $150 late fee.