Key takeaways
- Form K-120S is required from every S corporation with Kansas-source income, whether or not tax is due.
- For a 2026 calendar year, the federal Form 1120-S date is March 15, 2027 and the Kansas date works out to April 15, 2027.
- A federal Form 7004 attached to Form K-120S gives six months, but it does not move the shareholders' Form K-40 date.
- The Box N entity-level election is annual, irrevocable once made, and needs Form K-120ES estimates and a Form K-9 for each owner.
What Kansas requires from an S corporation
Kansas says Form K-120S must be completed by every enterprise with income or loss derived from Kansas sources, and that a corporation doing business in Kansas that must file a federal return files in Kansas whether or not tax is due.
The federal side is Form 1120-S, which exists only once the election is valid. The IRS says not to file it unless the corporation has filed or is attaching Form 2553, so confirm the acceptance letter is in the file first.
Tax year caveat: the Kansas figures here come from the 2024 and 2025 K-120S booklets. The 2026 booklet was not published when this was checked on 2026-11-10, so confirm the date and Box N rate against it.
Due date and extension for tax year 2026
Federal first. The Form 1120-S instructions give the 15th day of the 3rd month after year end. For the 2025 return that was March 16, 2026, because March 15, 2026 fell on a Sunday. For a 2026 calendar year it is March 15, 2027.
Kansas ties its date to the federal one. The 2025 K-120S instructions say a calendar-year filer files within one month after the federal due date, with payment of any liability due April 15, 2026. The 2024 booklet gave April 15, 2025. Following that pattern, the 2026 return and payment date is April 15, 2027, which is derived rather than published. A fiscal-year filer files by the 15th day of the fourth month after year end, and a weekend or holiday moves any date to the next regular workday.
For an extension, enclose a copy of federal Form 7004 with Form K-120S. Kansas has no separate request form, and the attachment gives an automatic six-month extension. Interest still applies to a balance paid late.
The trap is the owners. The extension does not extend a shareholder's Kansas Form K-40. A client whose K-1 is late because the entity is on extension still owes the personal return, or a personal extension, on the personal date.
Penalties and interest if the return is late
The 2025 Kansas instructions show a penalty of 1% per month or portion of a month, up to 24%, and interest of .6667% per month, which is 8% per annum. The 2024 instructions say paying at least 90% of the tax by the original due date avoids the penalty. An amount under $5.00 need not be paid.
For a non-electing S corporation there is usually little Kansas tax to attach those percentages to, so most of the exposure is federal. The Form 1120-S instructions put the penalty at $255 for each month or part of a month, up to 12 months, multiplied by the number of shareholders. Those are the 2025 instructions, so check the 2026 amount. Payment goes with Form K-120V, and Kansas says Form K-120S can be filed through IRS e-File.
The Box N entity-level tax election
Kansas lets an S corporation elect to pay tax at the entity level by marking Box N on Form K-120S. The Department's FAQ says the election may be made annually for tax years beginning on or after January 1, 2022, and that once made it is irrevocable and cannot be changed by an amended return.
The rate is the highest Kansas individual rate for 2024 and later years. The Department put it at 5.58% for 2024, and the 2025 booklet still multiplies line 31 by 5.58% on line 32. The rate was 5.7% for 2022 and 2023, when the Department's example was a $30,000 distributive share costing $1,710. At 5.58% the same share costs $1,674 (our arithmetic). A 2026 rate is not confirmed here.
Electing entities are treated as C corporations for estimated tax. Estimates are required for 2023 and later and can be paid with Form K-120ES or through the Kansas Tax Payment Portal. Because the election is irrevocable, decide before the first 2026 estimate, not on the return in 2027.
Eligible owners are individuals and trusts that file Form K-40 or Form K-41. A partnership or S corporation owner is not eligible, and neither is a single-member LLC taxed as an S corporation. If any shareholder is an entity, ask before recommending the election.
Each electing owner gets a Form K-9. It is not filed with Form K-120S; the owner attaches it to the personal Form K-40 or Form K-41. Under SB 410 from 2024, credits from the entity's activities pass through to the owners instead of being taken on Form K-120S.
Nonresident shareholders and composite returns
Kansas repealed nonresident withholding for S corporations for tax years beginning in 2014, and the forms KW-7, KW-7S, KW-7A and K-19 became obsolete. That comes from an older booklet, and the 2024 and 2025 booklets do not mention withholding. Delete any Kansas withholding line left in a client template.
What replaces it is reporting. In Part II of Form K-120S each shareholder carries a type code, and N means nonresident individual. For a nonresident with Kansas-only income, column 5 is column 4 times line 18. With income inside and outside Kansas, column 5 is column 4 times the sum of lines 22 and 23.
The S corporation can also file a composite return on Form K-40C and mark Box L on Form K-120S. Kansas says composite participants take the standard deduction and do not get their share of the entity's contribution deduction or credits. Decision rule: if a nonresident owner has other Kansas income or a large charitable deduction, leave that owner out and file individually.
What to collect from the client
Send the request in November, while the client can still change a Box N decision.
Shareholder list with state of residence on the last day of 2026, plus any move date. This sets the N codes in Part II. Ask this: "Did any shareholder move into or out of Kansas in 2026? If so, send the move date." Then record each answer.
Entity type for any shareholder that is not an individual, such as a trust, an LLC or another corporation. This decides Box N eligibility, and a trust must file Form K-40 or Form K-41 to be eligible.
The Form 2553 acceptance letter and the prior-year Form K-120S, which shows whether Box N or Box L was marked. Box N is annual, so last year does not bind this year.
Kansas estimate payments for 2026 with dates and confirmation numbers, from the portal or Form K-120ES. A missing payment shows up as an underpayment penalty figured on Schedule K-220S.
A split of 2026 sales, payroll and property between Kansas and other states. Part II uses lines 22 and 23 for income inside and outside Kansas, so one total will not do.
Failure modes and fixes
Failure: the Kansas date is set from the federal March date. Fix: use the Kansas date, one month later for a calendar-year filer, with the source and date checked beside it.
Failure: the client thinks the election can be undone on an amended return. Fix: Kansas says it cannot, so get the decision in writing before the first estimate.
Failure: the entity is on extension and the shareholders assume they are too. Fix: tell them Form K-40 keeps its own date.
Usual can hold the shareholder list, estimate confirmations and prior-year return in one request per client and send reminders on your schedule. The Kansas decisions still need a preparer.