Harper Tax CPA

Arizona S Corporation Extensions & Payments: IRS Form 1120-S + Arizona Form 120S (2026 Filing Season)

If you run an Arizona-based S corporation, “filing an extension” really means coordinating two tracks:

  1. Federal: IRS Form 1120-S (extended via Form 7004)
  2. Arizona: Arizona Form 120S (extended via Arizona Form 120/165EXT, and Arizona may also accept a valid federal extension)

Extensions give you more time to file—but generally not more time to pay. That’s where surprise penalties come from.

This guide covers deadlines, payment rules, and a clean checklist so you can extend correctly.

1) Key due dates for Arizona S corporations (Form 120S)

Arizona’s S corporation return (Form 120S) is due by the 15th day of the 3rd month after the close of the taxable year (for calendar-year S corps, that’s generally March 15).

2026 filing season note (calendar-year 2025 returns): March 15, 2026 is a Sunday, so the due date rolls to Monday, March 16, 2026 under the weekend/holiday rule.

If the due date lands on a weekend or legal holiday, Arizona treats the return as timely if filed the next business day.

2) Federal extension: Form 7004 for IRS Form 1120-S

To extend your IRS Form 1120-S, file Form 7004 by the original due date.

Important: extension ≠ extension to pay

The IRS is explicit: Form 7004 does not extend the time to pay any tax due.

Most S corporations don’t owe federal income tax at the entity level, but some do (see Section 4). If entity-level federal tax applies, you generally must pay by the original due date even if you extend.

3) Arizona extension: Arizona Form 120/165EXT (and when a federal extension works)

Arizona’s standard extension form is Arizona Form 120/165EXT (ADOR sometimes refers to it as “120EXT” on its website). It provides a maximum six-month extension to file and generally must be submitted by the original due date.

Arizona also indicates it will accept a valid federal extension for the same extension period.

Bottom line: Many Arizona S corporations still file Arizona Form 120/165EXT because it’s the cleanest way to (1) document the extension in Arizona’s system and (2) send any required extension payment.

4) “Do we owe anything?” (Often no—but watch these triggers)

Federal: when an S corporation might owe entity-level tax

Common federal scenarios include:

  • Built-in gains tax (if the S corp was previously a C corporation and recognizes built-in gains within the applicable recognition period)
  • Certain excess net passive income situations (generally tied to prior C corporation status)

If these apply, there may be entity-level federal tax on the 1120-S—and the payment is due by the original deadline even if you extend.

Arizona: when an Arizona S corporation might owe entity-level tax

Arizona generally treats S corporations as pass-through entities, but entity-level Arizona corporate income tax can arise in limited situations tied to corporate-level tax concepts on the federal 1120-S (for example, certain built-in gains/capital gain items taxed at the corporate level, or excess net passive income tax).

Also: if the S corp elects Arizona pass-through entity (PTE) tax, payment timing becomes a real entity-level compliance item.

So if your Arizona S corp is:

  • a “plain vanilla” pass-through with no corporate-level tax items, and
  • not making an Arizona PTE election,
    …it often has a filing extension but no entity-level Arizona payment due.

5) Arizona payments with an extension: the 90% rule + how to remit

Arizona is clear on two points:

  1. An extension is not an extension to pay.
  2. To avoid the extension underpayment penalty, you generally must pay at least 90% of the tax liability by the original due date.

Payment mechanics (Arizona)

  • Arizona Form 120/165EXT is used to transmit extension payments.
  • Arizona also has EFT requirements: if the taxpayer owes $500 or more, payment is generally required via EFT (subject to limited waiver rules).

Practical takeaway: If your S corp has entity-level tax exposure (built-in gains / excess net passive income tax / Arizona PTE election), treat extension time as extra filing time, not extra payment time.

6) The clean checklist: extend 1120-S + Arizona 120S the right way

Step 1 — Confirm what you’re extending

  • Federal: Form 1120-S (extension via Form 7004)
  • Arizona: Form 120S (extension via Arizona Form 120/165EXT, or rely on an accepted federal extension)

Step 2 — Estimate whether any entity-level tax is due

Look for:

  • Built-in gains / excess net passive income corporate-level tax items
  • Arizona PTE election implications (entity-level payments)

Step 3 — Pay what needs to be paid by the original due date

  • IRS: Form 7004 doesn’t extend time to pay
  • Arizona: extension doesn’t extend payment time; target 90% paid by the original due date to avoid underpayment penalty

Step 4 — File the extension(s) on time

  • Federal: Form 7004 by the original due date
  • Arizona: Arizona Form 120/165EXT by the original due date (or rely on the accepted federal extension—but keep clean documentation)

Step 5 — File the returns by the extended deadline

  • Arizona due date rule: 15th day of the 3rd month after year-end (then extended if a valid extension is in place)

7) Common Arizona S corp extension mistakes (that cause penalties)

  1. Assuming “extension” means “no payment due”
    Arizona explicitly treats an extension as an extension to file—not to pay.
  2. Extending the S corporation but forgetting shareholder-level needs
    Even if the S corp owes no entity-level tax, shareholders may need personal extensions and/or estimated payments.
  3. Not planning for Arizona PTE election cash flow
    If you elect PTE tax at the entity level, payment timing becomes a meaningful compliance item.

FAQ (Arizona S corp extensions)

Does Arizona require a separate extension if I filed federal Form 7004?
Arizona indicates it will accept a valid federal extension for the same period, but many filers still submit Arizona Form 120/165EXT to document the extension and submit any required payment cleanly.

Is the Arizona extension six months?
Yes—Arizona Form 120/165EXT provides a maximum six-month extension to file (for S corporations and partnerships).

If my S corp owes no entity-level tax, do I still need to pay anything with the extension?
Often no—but confirm you don’t have corporate-level tax items (built-in gains / excess net passive income) and you’re not paying Arizona PTE tax at the entity level.

 

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