Indiana keeps most filers on the April calendar but puts C-corporations a month later. For the 2025 tax year, individual, S-corporation, and partnership returns are due April 15, 2026, while the C-corporation return is due May 15, 2026. Indiana does not follow the federal March date for pass-throughs, and it layers county income taxes on top of the flat state rate.

What are Indiana's 2026 tax filing deadlines?

For the 2025 tax year, the Indiana individual return (IT-40), S-corporation return (IT-20S), and partnership return (IT-65) are due April 15, 2026, the 15th day of the fourth month. The C-corporation return (IT-20) is due May 15, 2026, because Indiana sets it one month after the federal due date. Indiana pass-throughs do not file on the federal March schedule.

How does Indiana's extension work?

A federal extension automatically grants an Indiana extension. For individuals, the extended filing deadline is November 16, 2026. The extension is to file only: you must pay at least 90% of the tax owed by April 15, 2026 to avoid penalty, with the balance and interest due by the extended date. Taxpayers without a federal extension use Form IT-9.

What is Indiana's pass-through entity tax (PTET)?

Indiana lets an S-corporation or partnership elect to pay Indiana income tax at the entity level, which moves the deduction above the federal SALT cap. The election is available for 2025 and is made by checking the PTET box on page 1 of the IT-20S or IT-65, with a fresh election required each year. The entity-level rate equals the individual rate, which is 3.00% for 2025. A valid PTET election also covers the nonresident individual composite requirement up to the tax paid.

How do county income taxes affect Indiana filings?

Indiana counties levy their own local income taxes in addition to the flat 3.00% state rate, and the county rate depends on where the taxpayer lives or works. The combined state-plus-county liability is what drives whether estimated payments are required. Pull the current county rate from the state's annual departmental notice rather than assuming a single figure.

Who owes Indiana estimated tax?

Individuals expecting to owe $1,000 or more in combined state and county tax after withholding pay quarterly on April 15, June 15, September 15, 2026, and January 15, 2027 (Form ES-40). The threshold is measured against the combined liability, not the state portion alone.

How does a firm handle Indiana at scale?

Two things to track. First, the split date: a workflow that batches all business returns together will mis-date the IT-20, which is due in May, against the IT-20S and IT-65, which are due in April. Second, the county tax is easy to underweight because it sits outside the flat state rate but still drives the estimated-payment threshold. Map the C-corp date separately and carry the county rate into each client's projection. See how we think about scaling tax prep workflows.

Where do these dates come from?

All deadlines and thresholds here trace to the Indiana Department of Revenue. Verify against the source before filing.