M15C: Additional Charge for Underpayment of Estimated Tax (2025)
Minnesota · Minnesota DOR · Used for tax years 2025
Minnesota Schedule M15C calculates a C corporation’s additional charge for underpayment of estimated tax for 2025. It compares required installments with payments made and calculates the charge reported on Form M4.
Who files this form
C corporations use 2025 Schedule M15C to determine the additional charge for underpayment of estimated tax.
You do not need to complete this schedule if:
- You are filing your first Minnesota tax return.
- Your 2025 tax on line 1 is less than $500. In this case, you owe no additional charge.
For line 1, use your 2025 Form M4, line 1, minus the credits on Form M4, lines 4, 5, 6, and 7.
When it's due
For the 2025 tax year, estimated tax installments are due on the 15th day of the third, sixth, ninth, and 12th months of the taxable year.
For a short 2025 taxable year, installments are due on the 15th day of the third, sixth, ninth, and final months. No installment is required for a short taxable year of fewer than four months.
If a due date falls on a weekend or legal holiday, payments made electronically or postmarked the next business day are considered timely.
For the 2025 additional-charge calculation, line 14 uses the date the underpayment is paid or the 15th day of the third month following the tax year, whichever is earlier.
What you'll need
Have these items available to complete the schedule:
- Your 2025 Form M4, including the tax on line 1 and credits on lines 4, 5, 6, and 7.
- Your 2024 Form M4, if filed, including the tax on line 1 and credits on lines 4, 5, and 6.
- Estimated tax payment amounts and dates, including any 2024 overpayment credited to your 2025 estimated tax account.
- The corporation or designated filer's name, FEIN, and Minnesota Tax ID.
If you use an alternative installment method, complete and attach Schedule A of federal Form 2220 with the Minnesota adjustments described in the instructions. If more than one payment was made for a required installment, attach a separate computation for each payment.
How to file
Attach Schedule M15C to your Form M4. Enter the total additional charge from Schedule M15C, line 17, on Form M4, line 16.
If you use an alternative method for any installment, attach the completed federal schedule to Schedule M15C. If more than one payment was made for a required installment, also attach a separate computation for each payment.
Common mistakes
- Not rounding amounts. Round to the nearest whole dollar.
- Completing the quarterly columns out of order. Complete lines 7 through 13 for one column before starting the next. In the first column only, enter line 6 directly on line 10.
- Leaving out a credited overpayment. Include any 2024 overpayment credited to your 2025 estimated tax account in the first column of line 6.
- Using prior-year tax when an exception applies. On line 3, use line 1 if you did not file a 2024 return, your preceding-year return covered less than 12 months, or you had no 2024 tax liability. Large corporations must follow the special instructions.
- Omitting required attachments. Attach Schedule M15C to Form M4, the federal schedule if you use an alternative method, and separate computations when more than one payment was made for a required installment.
Questions people ask
How much is each required installment?
Generally, each installment is 25 percent of line 3 unless you use an alternative method. For a short taxable year, divide line 3 by the number of installments due. Large corporations have special rules.
How is the additional charge calculated?
For each underpayment, line 16 multiplies the number of days on line 15, divided by 365, by .07 and the underpayment on line 12. Add the charges on line 17. Estimated tax payments are applied to underpayments in the order the installments were due.
Can I use a different method if my income varied during the year?
Yes. The instructions allow the Adjusted Seasonal Installment Method and the Annualized Income Installment Method. Complete Schedule A of federal Form 2220, make the listed Minnesota adjustments, and attach it to Schedule M15C.
What counts as a large corporation?
A corporation is considered large if its Minnesota taxable net income after apportionment was $1 million or more in any of the three tax years immediately preceding the current year. For a unitary business, the test uses the combined Minnesota taxable net income of its members.
Can a large corporation base installments on prior-year tax?
For the first quarter only, it may use 100 percent of the prior year's tax liability as the required annual payment. Any resulting reduction must be added to the second-quarter installment. The second, third, and fourth installments must be based on 100 percent of current-year tax liability unless an alternative method is used.