51: Estimated Payment of Individual Income Tax 2025 (2025)

Who files this form

Use Form 51 to:

• Calculate any payment needed for a valid tax year 2025 filing extension.
• Make estimated payments for tax year 2026.
• Pay Qualified Investment Exemption (QIE) recapture when you don’t file your income tax return by the due date.

Return the voucher only if you’re making a payment. For a 2025 filing extension, if the worksheet’s payment due is $50 or less, you don’t have to pay it now to get the extension.

When it's due

• April 15, 2026, for tax year 2025: If a payment is needed to qualify for a filing extension, pay online or have it postmarked by this date. Interest applies to any tax due that you don’t pay by this date.
• October 15, 2026, for tax year 2025: If you qualify for the extension, file and pay by this date. Penalties can apply.

There’s no extension for paying.

What you'll need

Have these records and details ready to complete the worksheet and voucher:

• Your 2024 Idaho Form 40 or Form 43, if you filed, to calculate the prior-year tax amount.
• Your estimated 2025 taxable income, additional income taxes, and income tax credits.
• Your Idaho income tax withholding and Form 51 payments for 2025.
• Your name, full Social Security number, and address. For a joint return, include your spouse’s name and full Social Security number.
• The payment amount and the tax year the payment is for.

How to file

For a 2025 extension payment, complete the Tax Payment Worksheet. Line 11 shows the minimum payment needed for a valid filing extension. You can add an extra payment on line 12 to reduce the tax you owe and the interest it will accrue. Enter the line 13 total on the voucher.

You can pay the extension amount online or mail the payment with the voucher. Mail to:

Idaho State Tax Commission

PO Box 83784

Boise ID 83707-3784

Keep the worksheet for your records. Return just the voucher, and only if you’re making a payment. Check the appropriate tax year on the voucher.

For a QIE recapture payment, write “Payment of QIE Recapture” at the bottom of the voucher and return it with a check.

Common mistakes

• Treating a filing extension as extra time to pay. There’s no payment extension. Interest applies to unpaid tax after April 15, 2026, for tax year 2025, and penalties can apply.
• Using the prior-year payment method when you’ve never filed in Idaho. The form says you can’t use that method in this situation.
• Sending the worksheet with the payment. Keep it for your records and return only the voucher.
• Sending a voucher without a payment. Return the voucher only if you’re making a payment.
• Not checking the payment year. Check the appropriate year on the voucher.
• Leaving off the QIE recapture label. For that payment, write “Payment of QIE Recapture” at the bottom of the voucher and return it with a check.

Questions people ask

How do I qualify for an automatic 2025 filing extension?

If you can’t file by April 15, 2026, you qualify if you pay at least 100% of the income tax on your 2024 return, if you filed, or 80% of the estimated tax due on your 2025 return. You can’t use the prior-year method if you’ve never filed in Idaho. Use the worksheet to calculate any payment due.

What if the worksheet shows a payment due of $50 or less?

You don’t have to pay that amount now to get the filing extension.

What if I didn’t file a 2024 tax return?

On worksheet line 7, enter the amount from line 6, which is 80% of line 5.

Can I use this form for 2026 estimated payments?

Yes. The form says it can be used for tax year 2026 estimated payments. Check the appropriate year on the voucher.

Does the filing extension stop interest from accruing?

No. For tax year 2025, interest applies to any tax due that you don’t pay by April 15, 2026. There’s no extension for paying.

Official sources

• https://tax.idaho.gov/wp-content/uploads/forms/EFO00092/EFO00092_09-18-2025.pdf