2026 Federal and State Tax Deadlines, and What Missing Each One Costs

September 15, 2026: the heaviest date left in the year

Two unrelated obligations fall on the same day, each with its own penalty. **Q3 2026 estimated tax**, on Form 1040-ES. Miss it and interest runs at 7% per year, compounded daily, from September 15 until you pay. There is no flat fine, so paying late is cheaper than not paying. **Extended 2025 S-corp and partnership returns**, Forms 1120-S and 1065, for calendar-year entities that filed Form 7004 back in March. Schedule K-1 has to reach every shareholder or partner by the same date. This penalty is the one people underestimate: $255 per owner per month or part month, up to 12 months, and it applies **even when the entity owes no tax at all**. A four-partner LLC three months late owes $3,060 on a return with a zero balance. If the return is more than 60 days late and tax is owed, a floor applies: the smaller of the tax due or $525.

October 15, 2026

**Extended individual return**, Form 1040 or 1040-SR, for anyone who filed Form 4868 by April 15. Also the extended Form 1120 for calendar-year C-corps and the extended FBAR (FinCEN 114), which auto-extends without a request. The point most often missed: Form 4868 extended the time to **file**, never the time to **pay**. Interest and the failure-to-pay penalty have been running on any unpaid 2025 balance since April 15. What October 15 starts is the separate and much larger failure-to-file penalty, at 5% of unpaid tax per month against 0.5% for failure to pay. Where both penalties apply in the same month, the failure-to-file penalty is reduced by the failure-to-pay penalty. Failure to file maxes out after five months at 25%; failure to pay keeps accruing.

November 2026 to January 2027

**Nov and Dec**: the year-end planning window. Roth conversions, tax-loss harvesting, charitable bunching, §199A QBI position checks, and the deferral election by December 31 for a Solo 401(k). **Dec 31** is also the last useful date for the withholding fix. Extra tax withheld from wages at any point in 2026 is treated under §6654(g) as paid a quarter on each of the four estimated tax due dates, including ones already passed. An estimated payment made in December only counts from December. Withholding in December counts across the whole year, which makes it the only way to retroactively cure a missed Q1 or Q2 installment. **Jan 15, 2027**: Q4 2026 estimated tax, the final installment for the 2026 year. **Feb 1, 2027**: W-2s and 1099-NECs due to recipients and filed with the SSA and IRS. January 31 is a Sunday in 2027, so the date shifts to the Monday.

What has already passed in 2026

**Jan 15**: Q4 2025 estimated tax. **Feb 2**: W-2 and 1099-NEC to recipients and to the SSA and IRS. January 31 fell on a Saturday in 2026. **Mar 16**: S-corp (1120-S) and partnership (1065) returns, or Form 7004 for the six-month extension to September 15. March 15 was a Sunday. **Mar 31**: electronically filed 1099-MISC to the IRS. **Apr 15**: Form 1040, Form 1120 for calendar-year C-corps, Q1 2026 estimated tax, last day for 2025 IRA, Roth IRA and HSA contributions, Form 4868 and Form 7004 extensions, and FBAR (auto-extended to October 15). **Apr 30, Jul 31**: Form 941 for Q1 and Q2. **Jun 15**: Q2 2026 estimated tax, and the automatic two-month filing extension for US citizens and residents living abroad. Interest still ran from April 15 on anything owed.

Payroll and sales tax, recurring

**Form 941**, the federal employer return, is quarterly and due the last day of the month following quarter end: April 30, July 31, November 2 (October 31 is a Saturday in 2026) and February 1, 2027. **Form 940** for FUTA is annual, due February 1, 2027 for the 2026 year. **State sales tax** varies by state and by volume: monthly, quarterly or annually, with high-volume sellers filing monthly and often carrying prepayment requirements.

State deadlines, the pattern and the exceptions

Most states tie the personal income tax deadline to the federal April 15. The exceptions that catch people: Hawaii on April 20, Virginia on May 1, Louisiana on May 15, Delaware corporate franchise tax on March 1, and California, where June 15 is the relevant entity payment date for several pass-through filings. State estimated tax quarterly dates usually mirror the federal April, June and September dates. Q4 is where they diverge, with a handful of states scheduling outside the federal January 15. Clearing the federal safe harbor does not clear a state one, and each state sets its own percentages.

Statute references

• Time and place for filing returns — IRC §6072
• Failure to file a return or to pay tax — IRC §6651
• Failure to file a partnership return — IRC §6698
• Failure to file an S corporation return — IRC §6699
• Determination of the interest rate — IRC §6621
• FBAR filing — 31 USC §5314 / 31 CFR §1010.350