How to Fill Out Montana Form IT: Individual Income Tax Payment Voucher

Montana Form IT is the Individual Income Tax Payment Voucher you mail with a check to the Montana Department of Revenue. It is not a tax return. The voucher is a short slip that tells the department whose account to credit and what the payment is for, and you use it any time you send a paper check for individual income tax, whether that payment goes with your Form 2 return, an extension, an estimated tax installment, or an amended return.1Montana Department of Revenue. Montana Individual Income Tax Payment Voucher Form IT

If you pay online through the TransAction Portal at tap.dor.mt.gov, skip Form IT entirely. The voucher exists only for mailed check payments.

When You Use Form IT

The voucher itself lists the four situations it covers:1Montana Department of Revenue. Montana Individual Income Tax Payment Voucher Form IT

  • A payment mailed with your annual Form 2 return because you owe tax.
  • An extension payment sent by the April filing deadline.
  • An estimated tax payment during the year.
  • A payment accompanying an amended return.

The extension case trips people up most often. Montana grants an automatic six-month extension to file your return, but that extension does not push back the payment deadline.2Montana State Legislature. Montana Code 15-30-2604 – Time for Filing – Extensions of Time If you expect to owe but your return isn’t ready, mail Form IT with your best estimate of the tax by April 15 to avoid penalties and interest.

How to Fill Out the Voucher

Form IT is a single detachable slip at the bottom of the page. The fields are short:

  • Tax year. Enter the year the payment covers. For a return filed in 2026, that’s 2025.
  • Social Security number. Enter yours, and your spouse’s if you file jointly.
  • Name and mailing address. Print it exactly as it appears on your Form 2.
  • Payment type. Check one box: return, extension, estimated, or amended.
  • Amount. Write the dollar amount of the enclosed check.

Double-check the Social Security number and the payment-type box before you detach the slip. Those two fields are what route the money to the right account and the right tax period. A wrong box can post an extension payment as an estimated payment, which creates a mismatch when your return is processed later.

How to Mail It

Detach the voucher along the perforation. Make your check payable to the Montana Department of Revenue. Do not staple the check to the voucher. Mail both to:

Montana Department of Revenue
PO Box 6309
Helena, MT 59604-63091Montana Department of Revenue. Montana Individual Income Tax Payment Voucher Form IT

Write your Social Security number and the tax year on the check itself. If the voucher and check ever get separated inside the mailroom, the information on the check is what lets the department still credit your account correctly.

Mailing the Voucher With a Return

If you’re sending Form IT together with your paper Form 2 because you owe tax, the return and the voucher go to a slightly different box than the voucher alone: PO Box 6308, Helena, MT 59604-6308 is the address for a return with a payment.3Montana Department of Revenue. Department of Revenue Mailing Addresses The voucher’s own PO Box 6309 address is set up for payments arriving on their own, such as an extension check or an estimated payment.1Montana Department of Revenue. Montana Individual Income Tax Payment Voucher Form IT Using the wrong box doesn’t lose your payment, but it can delay processing while the department sorts the paperwork internally.

If You’d Rather Pay Online

The TransAction Portal at tap.dor.mt.gov accepts individual income tax payments directly from a bank account. If you pay there, you do not file Form IT. The portal records the payment type, tax year, and account on your behalf, which is the same information the voucher captures for a mailed check.

Deadlines That Matter for a Form IT Payment

For the 2025 tax year, individual income tax payments are due April 15, 2026.4Montana Department of Revenue. 2025 Montana Form 2 Individual Income Tax Instructions This is the deadline that governs any Form IT payment labeled as a return payment or an extension payment. Estimated tax payments follow their own quarterly schedule.

If your check reaches the department after the due date, Montana charges a late payment penalty of 0.5% per month on the unpaid tax, calculated daily at 0.0164% per day and capped at 12% of the amount owed. Interest accrues on top of that at an annual rate of 7% for 2026, calculated daily from April 15 until the balance is paid.4Montana Department of Revenue. 2025 Montana Form 2 Individual Income Tax Instructions The late payment penalty can be waived if you pay the tax and interest within 30 days of the department’s first notice, or if you paid at least 90% of the year’s tax by the due date.

If you file the return itself late in addition to paying late, a separate late filing penalty applies: the greater of $50 or 5% of the tax due for each month the return is overdue, capped at 25% of the tax due.4Montana Department of Revenue. 2025 Montana Form 2 Individual Income Tax Instructions The automatic six-month extension prevents the filing penalty as long as you file by October 15, but it does nothing for the payment penalty if you underpaid in April.

Form IT Is Not Your Return

One point worth repeating because it causes real confusion: Form IT does not report income, calculate tax, or substitute for filing. Your actual Montana individual income tax return is Form 2, available on the Department of Revenue website.5Montana Department of Revenue. Montana Individual Income Tax Return Form 2 Mailing Form IT with a check pays the tax; it does not file the return. You still have to submit Form 2 — electronically through approved software or on paper to the appropriate PO Box — to meet your filing obligation.