Individual Return Deadlines
| Deadline | Date | Description |
|---|
| Individual return due | April 15, 2026 | Form 1040 federal; Form 540 California |
| Extension deadline | October 15, 2026 | Extended individual returns (federal and California) |
| IRA contribution deadline | April 15, 2026 | Traditional and Roth IRA contributions for 2025 |
| SEP-IRA contribution deadline | October 15, 2026 | If extension filed; otherwise April 15 |
| HSA contribution deadline | April 15, 2026 | Health Savings Account contributions for 2025 |
Business Return Deadlines
| Return | Original Due Date | Extended Due Date |
|---|
| S Corp (Form 1120-S) | March 16, 2026 | September 15, 2026 |
| Partnership (Form 1065) | March 16, 2026 | September 15, 2026 |
| C Corp (Form 1120) | April 15, 2026 | October 15, 2026 |
| California S Corp (Form 100S) | March 16, 2026 | October 15, 2026 |
| California LLC (Form 568) | April 15, 2026 | November 15, 2026 |
Payroll Tax Deadlines
| Filing | Due Date |
|---|
| W-2s to employees | January 31, 2026 |
| 1099-NECs to contractors | January 31, 2026 |
| W-2s / 1099s to IRS/SSA | January 31, 2026 |
| Q4 2025 payroll tax return (Form 941) | January 31, 2026 |
| Q1 2026 payroll tax return (Form 941) | April 30, 2026 |
| Q2 2026 payroll tax return (Form 941) | July 31, 2026 |
| Q3 2026 payroll tax return (Form 941) | October 31, 2026 |
| Annual FUTA return (Form 940) | January 31, 2026 |
Estimated Tax Deadlines
| Quarter | Federal & California Due Date |
|---|
| Q1 2026 | April 15, 2026 |
| Q2 2026 | June 15, 2026 |
| Q3 2026 | September 15, 2026 |
| Q4 2026 | January 15, 2027 |
California-Specific Deadlines
California has several deadlines that differ from or are in addition to federal deadlines: the $800 California franchise tax is due April 15 regardless of extension status; California Form 568 (LLC return) is due April 15 with a 7-month extension to November 15; California Form 3840 (1031 exchange annual report) is due with your California return; and the California PTET election must be made by June 15 of the tax year.
Penalties for Missing Deadlines
Missing tax deadlines is expensive. The failure-to-file penalty is 5% per month (up to 25%) of unpaid tax. The failure-to-pay penalty is 0.5% per month (up to 25%). Combined, these penalties can add 47.5% to your tax liability. For business returns, the late filing penalty is $235 per month per shareholder/partner (up to 12 months). KDA maintains a filing calendar for every client and files extensions proactively to prevent these penalties.
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