2027 Idaho Tax Deadlines

Last updated: July 29, 2026

Key Idaho tax dates at a glance

This block is the single date reference for 2027 Idaho filing, payment, estimated-payment, and extension planning.

• April 15, 2027: First Idaho estimated payment for calendar-year taxpayers.
• June 15, 2027: Second Idaho estimated payment.
• September 15, 2027: Third Idaho estimated payment.
• January 18, 2028: Fourth Idaho estimated payment.
• April 18, 2028: Idaho Individual, C Corporation, S Corporation, and Partnership returns and balances due for calendar-year filers.
• October 16, 2028: Extended Idaho Individual, C Corporation, S Corporation, and Partnership returns due; payment is not extended.

When are Idaho taxes due in 2027?

Idaho's 2027 calendar-year Individual, C Corporation, S Corporation, and Partnership returns are generally due April 18, 2028. Estimated payments run during the tax year, and extensions move filing only to October 2028. Idaho currently applies a flat 5.3% Individual income-tax rate under the latest Tax Commission schedule; reconfirm the tax-year 2027 rate when the 2027 instructions are issued.

When are Idaho C Corporation taxes due for 2027?

Idaho C Corporations file Form 41 by April 18, 2028, and pay the expected balance by April 18, 2028. Idaho C Corporations file on the fourth month of the calendar year. Use approved software for supported returns and keep Idaho Taxpayer Access Point confirmations with the return workpapers.

What does the Idaho C Corporation extension change?

The extended filing deadline for a calendar-year Idaho C Corporation return is October 16, 2028. The extension gives more time to file, not more time to pay, so the expected balance remains due April 18, 2028.

When are Idaho S Corporation and Partnership taxes due for 2027?

Idaho S Corporations file Form 41S and Partnerships file Form 65 by April 18, 2028.

What pass-through payment rules should teams watch?

Eligible S Corporations and Partnerships may make Idaho's affected-business-entity election using Form ABE. To qualify for the automatic extension, the entity generally must pay 100% of prior-year Idaho tax or, if there was no prior-year Idaho return, 80% of current-year Idaho tax by the original due date using Form ABE-ES. The projected extended filing deadline is October 16, 2028; payment and election deadlines are not automatically postponed.

When are Idaho Individual taxes due for 2027?

An Idaho Individual return using Form 40 for residents and Form 43 for part-year residents and nonresidents is due by April 18, 2028, and any remaining state income tax should be paid by April 18, 2028.

When is the Idaho Individual extension deadline?

The extended filing deadline for a 2027 Idaho Individual income tax return is October 16, 2028. The extension applies to filing only, so the payment deadline remains April 18, 2028.

When are Idaho estimated payments due?

Calendar-year Idaho estimated payments are due on this schedule:

• April 15, 2027.
• June 15, 2027.
• September 15, 2027.
• January 18, 2028.

Who must make Idaho estimated payments?

Taxpayers who expect an Idaho income-tax balance after withholding and credits may need estimated payments. Apply the tax-year 2027 threshold, safe-harbor, and voucher instructions when the filing-year guidance is released. Use Form 51 for Idaho estimated income tax payments when the Tax Commission instructions require a voucher.

What Idaho rules should tax professionals watch for 2027?

Beyond the core due dates, Idaho has several pass-through and filing-calendar rules worth checking before 2027 work begins:

How does Idaho's affected business entity election affect pass-through returns?

Form ABE can move qualifying owner-level tax to the entity, adding an election, estimated-payment, and owner-reporting track to the annual pass-through return.

Why does Idaho use a fourth-month filing calendar?

Idaho aligns calendar-year business and Individual income-tax returns to the 15th day of the fourth month, with weekend and holiday roll-forward rules moving the 2027 filing-year due date to April 18, 2028.

How should teams handle Idaho TAP and electronic filing?

Idaho Taxpayer Access Point supports eligible filings, payments, account work, and correspondence. Tax teams should save submission and payment confirmations as evidence of the deadline.

Tax-professional context: Idaho return calendars, entity-level elections, owner reporting, withholding, and payment rules require a state-specific review. TY2027 forms and the final 2028 filing calendar remain subject to confirmation when the state publishes them.

Electronic filing requirements: Idaho uses Idaho Taxpayer Access Point for supported account management, filing, correspondence, and payment services. Use approved software for supported corporate, pass-through, and Individual returns. Use Idaho Taxpayer Access Point for eligible payments and account work. Review state electronic-filing mandates separately from federal requirements. Keep proof of timely electronic submission and payment with the workpapers.

Electronic account management: Idaho Taxpayer Access Point supports eligible filings, payments, account access, and correspondence.

What sources support these Idaho deadlines?

• Idaho Business Income Tax Filing and Paying.
• Idaho Extensions.
• Idaho Income Tax Forms.
• Idaho Affected Business Entity Guidance.

Idaho estimates and entity filing deadlines

Idaho teams need to coordinate entity returns, pass-through guidance, withholding, and estimated payments without treating each deadline as a separate checklist. Instead's AI-driven tax platform keeps the calendar connected to the work.

Use filing for return execution, estimates for payment planning, and fixed-assets support for repeatable review steps across Idaho clients. Built for tax professionals who want a better tax operation system to manage compliance and advisory work for clients.