Idaho State Tax Commission

Valid Extension for Filing

If you can't file your income tax return by the due date, you can file your return up to six months late with a valid extension.

A valid extension means you can avoid a penalty for filing late. There aren't any extensions allowing you to pay late. You'll owe interest on any payments made after the original due date. You'll also owe penalties if you pay after the extended due date (six months after the original due date).

Ensuring you have a valid extension

We have two worksheets to help you make sure you have a valid extension to file late:

After you finish the worksheet, do one of the following:

  • If you need to make a payment, you can mail the form at the bottom of the worksheet with your check. Or, you can use our free, secure QuickPay service online to authorize a payment from your bank account.
  • If you don't need to make a payment, you don't have to send us Form 51 or Form 41ES. Just be sure to file your income tax return by the extended due date.
What to do if you don't have a valid extension

If it's after the original due date and you don't have a valid extension:

  • File your income tax return as soon as possible.
  • Pay as much as you can now. (Pay the entire amount due if possible.) See our E-Pay page for options.

These steps can greatly reduce the amount of interest and penalties you owe.

More information about interest and penalty

You'll owe interest and penalties on all overdue tax payments. Idaho law requires us to charge interest, and we can't waive it.

Interest rates change each year. See the interest rates chart.

Penalties can vary from 0.5% per month to a maximum of 50% of the tax due. See the Penalties and Interest guide for the different kinds of penalties and how they're calculated.

You can use our Penalty and Interest Estimator to calculate what you could owe.

Last updated September 30, 2019. Last full review of page September 30, 2019.

This information is for general guidance only. Tax laws are complex and change regularly. We can't cover every circumstance in our guides. This guidance may not apply to your situation. Please contact us with any questions. We work to provide current and accurate information. But some information could have technical inaccuracies or typographical errors. If there's a conflict between current tax law and this information, current tax law will govern.