Kansas has a distinctive rule that produces two common errors: every Kansas business return is due one month after the federal deadline. That pushes the corporate return to May and pass-throughs to April — not the federal March date.

Kansas Tax Deadlines at a Glance (2026)

The root of both corrections: Kansas business returns are due one month after the federal due date. So the C-corporation K-120 is due May 15, 2026 (a month after the federal April 15), extending to November 15, and the S-corp/partnership K-120S is due April 15, 2026 (a month after the federal March 15), extending to October 15. Copying the federal dates onto a Kansas return is the frequent mistake; tax owed is still due at the original date.

Rates and the SALT Parity PTE Tax

Kansas has a two-bracket individual income tax: 5.2% and a 5.58% top rate (over $46,000 married / $23,000 single). The corporate rate is 3.5% plus a 3.0% surtax on income over $50,000, for a 6.5% top rate. Under the SALT Parity Act, S corporations and partnerships may elect to pay at the entity level — at the top individual rate, 5.58% for 2025 — with owners receiving a credit.

Estimates, Extensions, and Penalties

Individual estimated payments (K-40ES) are due April 15, June 15, September 15, 2026, and January 15, 2027. The 2026 interest rate on underpayments is 8% per year (0.6667% per month); the individual late-payment penalty is 1% per month, up to 24%. An extension covers filing only.

CPA Action Steps

• Use May 15 for the C-corp K-120 (one month after federal)

• File K-120S pass-through returns in April, not on the federal March date

• Apply the two-bracket 5.2%/5.58% individual and 6.5% corporate rates

• Consider the SALT Parity PTE election at 5.58%

Verify current rates and dates against the Kansas Department of Revenue (ksrevenue.gov) before filing.