80-320: Interest and Penalty Worksheet (2025)
Mississippi · Mississippi DOR · Used for tax years 2025
Mississippi Form 80-320 is the 2025 Individual Income Tax Interest and Penalty Worksheet. It calculates interest on underpaid estimated tax, late filing and late payment charges, and the first-time home buyer penalty for resident and nonresident or part-year resident returns.
Who files this form
Use Form 80-320 to calculate interest on underpaid estimated tax if your 2025 Mississippi income tax liability exceeds $200. If that liability is $200 or less, the instructions say no interest is due on the underestimate of tax.
The worksheet also calculates first-time home buyer penalties, late filing penalties, and late payment interest and penalties for:
- Residents filing Form 80-105.
- Nonresidents and part-year residents filing Form 80-205.
The form lists an exception for taxpayers whose farming or fishing income is at least two-thirds of total gross income, if they meet the stated payment or filing conditions.
When it's due
For tax year 2025, the worksheet lists these estimated tax payment due dates:
- April 15, 2025.
- June 15, 2025.
- September 15, 2025.
- January 15, 2026.
These dates are used in columns A through D to calculate interest on underpaid estimated tax.
What you'll need
Have these forms and records available to complete the applicable parts of the worksheet:
- Your 2025 Mississippi return: Form 80-105, line 20, or Form 80-205, line 22, for your net income tax liability.
- Your 2024 Mississippi return: Form 80-105, line 21, or Form 80-205, line 23, for your prior-year net income tax liability.
- Payment records: Mississippi income tax withheld, estimated tax payments as of each payment due date, and any prior-year overpayment.
- Your balance due: Form 80-105, line 35, or Form 80-205, line 36, for late filing and late payment calculations.
- Form 80-108, Part V, Schedule N, line 2: if calculating a first-time home buyer penalty.
The worksheet also asks for your name, Social Security number, mailing address, county code, and spouse information.
Common mistakes
- Putting withholding in the wrong column: Enter income tax withheld in column A only. The instructions also place the prior-year overpayment in column A.
- Missing carryforwards: Carry any overpayment or underpayment from line 8 to line 7 of the next column. Show overpayments as negative amounts and underpayments as positive amounts.
- Calculating interest on a negative amount: If line 8 is negative, enter zero on line 10.
- Leaving out an explanation: If filing requirements were met after a payment due date, compute interest in the applicable columns and provide an explanation.
- Forgetting to transfer the total: Enter line 19 on Form 80-105, line 36, or Form 80-205, line 37.
Questions people ask
What interest rate applies to underpaid estimated tax?
The worksheet uses 1/2% per month, from the payment due date until the amount is paid or the next payment due date, whichever is earlier.
How is the late filing penalty calculated?
The penalty is 5% per month on the net tax due, up to 25% in total. The minimum penalty is $100.
How are late payment interest and penalties calculated?
Both are calculated on the balance due on line 15. Interest is 1/2% per month. The penalty is also 1/2% per month, but is capped at 25% in total.
What is the first-time home buyer penalty?
The penalty is 10% for withdrawals for unqualified expenses, using the amount from Form 80-108, Part V, Schedule N, line 2. The worksheet refers readers to the Form 80-100 instruction booklet for more details.
How do I calculate the total interest and penalty?
Add lines 11, 12, 14, and 18 and enter the result on line 19. Also enter it on Form 80-105, line 36, or Form 80-205, line 37.