How to pay Idaho estimated taxes.

Idaho collects its own estimated tax through the Idaho State Tax Commission, separate from the IRS. Here’s who needs to pay, when, and how to pay online.

Do you need to pay?

Idaho does not require individuals to make estimated tax payments. You can make voluntary payments at any time with Form 51 or Quick Pay.

There is no estimated tax underpayment penalty because estimates are not required. To have a valid extension and avoid the late filing penalty, your prepayments (withholding, estimated payments, applied refunds) must equal at least 80% of your current year tax or 100% of the tax on your prior year return. If you did not file the prior year, you must meet the 80% test.

If you underpay: No estimated tax underpayment penalty. Interest on unpaid tax is 6% a year for 2026.

For how to pick a safe amount, see how much to pay in estimated taxes.

Deadlines

Idaho has no required installment schedule. You can pay whenever you like during the year. Many people still pay on the federal dates (April 15, June 15, September 15, January 15) so the money is in before the April filing deadline.

A date on a weekend or holiday moves to the next business day. Pay at least two business days early.

Paying Idaho, step by step

What you need

Nothing to set up. Idaho E-Pay takes payments without an account.
Your Social Security number and a copy of last year's Idaho return.
Your bank routing and account numbers.

Start at Idaho E-Pay, Idaho's official payment site.

Click Quick Pay. No account is needed.
Select Individual Income Tax as the tax type.
Choose the payment type (Estimated Single) if you file single, or (Estimated Joint) if you file jointly.
Enter your identifying information, the tax year, and the amount.
Pay from your bank account (no fee) or by card, then save your confirmation.

Other ways to pay: Mail Form 51 with a check or money order, pay in person at a Tax Commission office, or pay through a TAP account (which lets you schedule payments up to a year ahead). Card payments carry a 2.5% service fee; bank account (ACH debit) payments are free.

Idaho will not fill these payments in for you. Your preparer has to enter each estimated payment on your Idaho return. Keep your own record of the date, amount, and confirmation number.

Extension payments

Idaho gives an automatic six-month extension to file, with no form to file, but only if your prepayments meet the 80% current year or 100% prior year test by April 15. If the payment needed to reach that amount is $50 or less, you don't have to pay it to get the extension. The extension does not extend the time to pay. Use the Form 51 worksheet to figure the payment, then pay through Quick Pay or mail the Form 51 voucher with a check.

Make this year's first estimated payment as a separate transaction, marked as an estimate for the current year.

Good to know

Estimated payments are optional for individuals, but the 80%/100% prepayment test decides whether your extension is valid.
Interest runs on any tax not paid by April 15, even with a valid extension.
Idaho's rule requiring ACH for payments of $100,000 or more does not apply to individual income tax payments.
Paying other states? See the payment links for every state's official site, and the federal walkthrough.

Official sources

Checked October 2026 against the Idaho State Tax Commission's own publications.

This guide is for general education and reflects rules as of October 2026. Tax law and agency websites change, and your situation may have details that change the answer. Please talk with your tax professional before acting on it.