Idaho tax deadlines in 2026: filing dates and estimated payments
Deadlines that fall in calendar 2026: the 2025 return and the 2026 estimated payments. Different year? See Idaho 2025 →
Idaho deadlines in 2026
| 2025 individual return due | April 15, 2026 |
|---|---|
| Extended filing deadline | October 15, 2026 |
| Payment due | April 15, 2026, extension or not |
| 2026 estimated payments | Not required; prepayments optional |
Conforms to the federal deadline.
Idaho estimated tax payments in 2026
Never required: Idaho does not require estimated tax payments from individuals; payments are voluntary and can be made at any time.
| Voucher | Form 51 (Estimated Payment of Individual Income Tax) |
|---|---|
| Underpayment safe harbor | Not applicable (no underpayment-of-estimated-tax penalty for individuals); for an automatic filing extension you must pay at least 100% of the prior-year tax or 80% of the current-year estimated tax by April 15. |
| Pay online | idahotap.gentax.com |
No installment schedule; Idaho publishes no quarterly due dates for individuals. Form 51 (EFO00092, rev. 09-18-2025) has checkboxes for tax year 2025 (extension) and 2026 (estimated payments). Online payment options are Quick Pay (no login) or Taxpayer Access Point (idahotap.gentax.com/TAP/_/).
Source: tax.idaho.gov, read September 3, 2026. “Idaho doesn't require estimated tax payments from individuals, but you can make payments at any time using either of these methods:”
All 51 jurisdictions in one table: state estimated tax payment dates for 2026.
Idaho extensions
Every state's rule in one table: which states accept the federal extension in 2026.
| Does Idaho accept the federal extension? | Not the federal one. The state extension is automatic when the required payment is made by the original due date. |
|---|---|
| Original due date | April 15, 2026 |
| Extended due date | October 15, 2026 |
| Payment | Still due April 15, 2026. The extension is to file, not to pay. A valid extension avoids the late-filing penalty only; interest is owed on any tax not paid by April 15 and penalties apply if prepayments fall short. |
| How to get it | Nothing to file; the extension is valid if prepayments equal 80% of the current-year tax or 100% of last year's tax by April 15 (use Form 51 worksheet/voucher to pay any shortfall). |
No payment is needed if the required amount is $50 or less; the federal Form 4868 is not part of the Idaho rule.
Source: tax.idaho.gov, read September 3, 2026. “To avoid the late filing penalty, your prepayments ... must equal either: 80% of the estimated tax due for your current return 100% of the income tax reported on your return for the previous year”
Federal deadlines in 2026
| 2025 Form 1040 | April 15, 2026 · extension October 15, 2026 |
|---|---|
| 2025 S-corp (1120-S) & partnership (1065) | March 16, 2026 |
| 2025 C-corp (Form 1120) | April 15, 2026 |
| 2026 federal estimated payments (1040-ES) | April 15, 2026 · June 15, 2026 · September 15, 2026 · January 15, 2027 |
Source: IRS Publication 509 and Form 1040-ES instructions, irs.gov.
Frequently asked questions
When are Idaho state taxes due in 2026?
Your 2025 Idaho individual income tax return is due April 15, 2026. If that date falls on a weekend or legal holiday, the deadline moves to the next business day. An extension moves the filing deadline to October 15, 2026, but any tax owed is still due on the original date.
When are Idaho estimated tax payments due in 2026?
Idaho does not require quarterly estimated payments from individuals; prepayments are optional. Use Form 51 (Estimated Payment of Individual Income Tax) or pay online. The final installment for 2025 was due January 15, 2026.
Does Idaho accept the federal extension?
Not the federal one. The state extension is automatic when the required payment is made by the original due date. The extended filing deadline is October 15, 2026, and tax is still due by April 15, 2026.
Does a Idaho extension give me more time to pay?
No. An extension extends the time to file, not to pay. To avoid penalties and interest, pay what you expect to owe by April 15, 2026.
Dates are the statutory deadlines that fall in 2026 and move to the next business day when they land on a weekend or holiday. Each section links to the source it was checked against. Always confirm with the Idaho tax agency or the IRS before relying on a date. This is general information, not tax advice.