Colorado runs almost everything off one date. Individual, C-corporation, and pass-through returns for the 2025 tax year are all due April 15, 2026, and the state grants an automatic six-month extension to file. The one number worth circling early: Colorado partnerships and S-corporations file on April 15, not the federal March deadline. That single difference is where most multistate workpapers go wrong.

What are Colorado's 2026 tax filing deadlines?

For the 2025 tax year, Colorado individual returns (DR 0104), C-corporation returns (DR 0112), and pass-through returns (DR 0106) are all due April 15, 2026. Colorado does not follow the federal March 15 date for S-corporations and partnerships.

How does Colorado's extension work?

The extension is automatic and there is no form to file. If you pay at least 90% of the tax owed by April 15, 2026, you have until October 15, 2026 to file the return. The extension covers filing only, not payment. Any balance left after April 15 accrues interest, and falling under the 90% threshold adds a penalty. Individuals pay through Revenue Online or Form DR 0158-I; C-corporations use DR 0158-C.

What is the SALT Parity (PTE) election, and is it still available?

Colorado's SALT Parity Act lets a partnership or S-corporation elect to pay Colorado income tax at the entity level, which moves the deduction above the federal SALT cap. The election is available for the 2025 tax year and is made on the DR 0106, by pre-filing Form DR 1705, or by paying with the DR 0106EP. It is annual, irrevocable once made, and binds every owner. One timing note for 2025 planning: the current statutory window covers tax years before January 1, 2026, so 2025 is the last year authorized under the present rules. Confirm the legislature's treatment of 2026 before advising clients to rely on it next year.

Who owes Colorado estimated tax?

Individuals expecting to owe more than $1,000 in net Colorado tax make quarterly payments on April 15, June 15, September 15, 2026, and January 15, 2027 (Form DR 0104EP). C-corporations expecting to owe more than $5,000 pay on April 15, June 15, September 15, and December 15, 2026 (Form DR 0112EP). Note the corporate fourth quarter lands in December, not January.

How does a firm handle Colorado at scale?

The trap is the calendar. A 200-return shop that batches all pass-throughs to a March 15 federal deadline will mis-date every Colorado DR 0106 unless the state due date is tracked separately from the federal one. Build the state-specific date into the workflow, flag SALT Parity clients before year-end because the election payment timing matters, and the April 15 convergence stops being a surprise. If you are reconciling federal and state pass-through dates by hand across a client book, that reconciliation is the kind of step worth automating. See how we think about scaling tax prep workflows.

Where do these dates come from?

All deadlines and thresholds here trace to the Colorado Department of Revenue. Verify against the source before filing, since rates and windows change.