Idaho State Tax Guide
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Idaho State Tax Guide
Extension rules
Extension type: Automatic — no separate state request required · Form 51 (payment only)
Idaho grants an automatic 6-month extension to file — no form required — if you have paid at least 80% of the current year tax or 100% of the prior year tax by April 15. Otherwise interest and a late-payment penalty apply.
The Idaho extension extends the time to file, not the time to pay. Pay the balance due by the payment deadline to avoid penalties and interest.
Idaho Key deadlines (tax year 2025, return filed in 2026)
- Filing deadline: Apr 15, 2026
- Extension request deadline: Apr 15, 2026
- Extended return deadline: Oct 15, 2026 (6-month extension)
- Payment deadline: Apr 15, 2026
- Differs from federal: No
Interest and penalties accrue on any unpaid balance after this date, even with a valid extension.
When a deadline falls on a weekend or legal holiday, it moves to the next business day.
Estimated payments
- Apr 15, 2026
- Jun 15, 2026
- Sep 15, 2026
- Jan 15, 2027
Payment rules
Pay any balance due to Idaho State Tax Commission by the payment deadline. Electronic payments post fastest; include the payment voucher when paying by check.
Official payment portal
Quick Pay (bank transfer) · Electronic payment
Payment options
- Quick Pay (bank transfer) · Free
- Credit / debit card · Processor fee applies
- Payment plan request
- Check with Form ID-VP voucher
Payment plan availability
Available: Yes
Installment payment plans are available by request through Idaho State Tax Commission.
Filing forms
Regular filing
- Form 40 - Idaho individual income tax return
- Form 43 - Supporting schedule or payment voucher
- ID-VP - Supporting schedule or payment voucher
Extension
- Form 51 - Request for extension of time to file
Idaho Refund Tracking
| Filing method | Typical processing time |
|---|---|
| E-file | 7–8 weeks |
| Paper | 10–11 weeks |
| Amended | Amended or manually reviewed returns take longer. |
Do I need to file?
You generally must file a Idaho return if you are required to file a federal return and your Idaho-source income exceeds the state's filing thresholds.
- Residents: Residents with gross income above the filing threshold must file Form 40.
- Part-year residents: Part-year residents file Form 43.
- Nonresidents: Nonresidents with Idaho-source income file Form 43.
- Flat 5.3% state income tax rate (2025).
- Grocery credit and property tax reduction (circuit breaker) may apply.
Official filing requirements — Idaho State Tax Commission
Thresholds change annually. Confirm your situation against current Idaho State Tax Commission guidance.
Filing methods
Online filing
Residents can file electronically using approved e-file providers or tax software such as FileTax, or through Idaho State Tax Commission online services.
Recommended — e-filed returns are processed ahead of paper returns.
Mail filing
Paper returns may be mailed following Idaho State Tax Commission instructions using Form 40.
Paper returns generally process slower than e-filed returns.
