Mississippi genuinely aligns with the federal calendar — including the March pass-through deadline — and is on a long phasedown of its individual income tax toward eventual elimination. Its corporate tax remains graduated, and it offers an elective pass-through entity tax.

Mississippi Tax Deadlines at a Glance (2026)

Mississippi’s dates track the federal calendar exactly: individuals and C corporations file by April 15, and S corporations and partnerships (Form 84-105) follow the third-month deadline of March 16, 2026 (March 15 is a Sunday), extending to September 15. Mississippi accepts the federal extension; remit any balance due with Form 83-180.

The Individual Rate Phasedown

Mississippi exempts the first $10,000 of taxable income and taxes the remainder at a flat 4.4% for 2025. Under the 2025 “Build Up Mississippi Act,” that rate steps down — 3.75% in 2027, 3.5% in 2028, and toward 3.0% by 2030, with revenue-triggered cuts aimed at eventual elimination of the individual income tax.

Corporate Tax and the Elective PTE

Mississippi’s corporate income tax is graduated — 0% on the first $5,000, 4% on the next $5,000, and 5% over $10,000 — so it is not a flat 5%; the 4% bracket is still in effect for 2025. A separate franchise tax ($0.75 per $1,000 of capital over $100,000) is being phased out and repealed effective 2028. Mississippi’s elective pass-through entity tax (Form 84-381) taxes electing entities at the same graduated schedule, with owners receiving a credit.

Estimates, Extensions, and Penalties

Individual estimated payments are due April 15, June 15, September 15, 2026, and January 15, 2027, required if annual liability exceeds $200. The late-payment penalty and interest each run 0.5% per month (interest capped in the aggregate). An extension covers filing only, not payment.

CPA Action Steps

• File S-corp and partnership returns by March 16 — Mississippi does follow the federal date

• Apply the flat 4.4% individual rate (first $10K exempt) for 2025

• Use the graduated 0/4/5% corporate schedule, not a flat 5%

• Consider the elective PTE (Form 84-381)

Verify current rates and dates against the Mississippi Department of Revenue (dor.ms.gov) before filing.