State Tax Calendar
Idaho 2025 Tax Deadline Calendar
Complete filing deadlines for Idaho individual, S-Corp, partnership, and corporate returns.
How Idaho Differs from Federal
- →Generally follows federal calendar — Idaho individual, S-Corp, and partnership deadlines mirror IRS deadlines.
- →Extension payment required — Idaho requires Form 51 (Estimated Payment of Idaho Individual Income Tax) if you owe tax and need an extension. Filing the federal extension alone is not sufficient if you have a balance due.
- →Top income tax rate: 5.8% (flat rate effective 2023). Idaho has a state sales tax of 6%.
- →S-Corp returns (Form 41S) due March 15, with extension to September 15.
2025 Idaho Filing Calendar
| Date | Filing / Payment Type | Entity Type | Notes |
|---|---|---|---|
| Jan 15 | Q4 2024 Estimated Tax | Individuals / Sole Props | Same as federal |
| Jan 31 | W-2 / 1099-NEC to State | All Employers | File with Idaho State Tax Commission |
| Mar 15 | S-Corp Return (Form 41S) | S-Corporations | Extension to Sep 15 |
| Mar 15 | Partnership Return (Form 65) | Partnerships | Extension to Sep 15 |
| Apr 15 | Individual Income Tax (Form 40) | Individuals | Extension to Oct 15 (Form 51 if balance due) |
| Apr 15 | C-Corp Return (Form 41) | C-Corporations | Extension to Oct 15 |
| Apr 15 | Q1 2025 Estimated Tax | Individuals / Sole Props | Same as federal |
| Jun 16 | Q2 2025 Estimated Tax | Individuals / Sole Props | Same as federal |
| Sep 15 | Q3 2025 Estimated Tax | Individuals / Sole Props | Same as federal |
| Sep 15 | Extended S-Corp / Partnership Returns | S-Corps / Partnerships | Final — no further extension |
| Oct 15 | Extended Individual Return (Form 40) | Individuals | Final deadline |
| Oct 15 | Extended C-Corp Return (Form 41) | C-Corporations | Final deadline |
| Jan 15, 2026 | Q4 2025 Estimated Tax | Individuals / Sole Props | Same as federal |
Idaho-Specific Tax Rules
Form 51 for Extensions
If you owe Idaho tax and need an extension, you must file Form 51 and pay the balance due by April 15 to avoid penalties — a federal extension alone is not enough.
Flat 5.8% Income Tax
Idaho moved to a flat 5.8% income tax rate in 2023. This applies to all taxable income for individuals and corporations.
Sales Tax: 6%
Idaho's state sales tax is 6%. Some cities add a local option tax. Food is exempt from sales tax in Idaho.
Non-Resident Withholding
Idaho requires 7.4% withholding on distributions to non-resident partners and S-Corp shareholders who have not filed a composite return.
Federal vs. Idaho — Quick Comparison
| Filing Type | Federal | Idaho |
|---|---|---|
| Individual Return | April 15 | April 15 (same) |
| S-Corp Return | March 15 | March 15 (same) |
| Partnership Return | March 15 | March 15 (same) |
| C-Corp Return | April 15 | April 15 (same) |
| Individual Extension | October 15 | October 15 (Form 51 required if balance due) |
| S-Corp Extension | September 15 | September 15 (same) |
| W-2 / 1099-NEC to State | January 31 | January 31 (same) |
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