Every 2026 federal tax deadline and IRS penalty rate, in one table

Where the IRS prints the date, the row says so. Where it prints a rule, the row gives the rule and the 2026 date it produces; a due date that lands on a Saturday, Sunday or legal holiday moves to the next business day, which is why 31 January becomes 2 February and 15 March becomes 16 March this year.

These are the rates for returns due after 31 December 2025 and for the quarter from 1 October 2026, read from the IRS penalty pages and the fourth-quarter interest rate release.

The year front-loads. Seven separate filings fall on 2 February 2026: W-2 copies to employees, W-2s and W-3 to the Social Security Administration, 1099-NECs to contractors and the IRS, the fourth-quarter Form 941, the annual Form 940, and Forms 944 and 945 for the employers that file them. A business that has not reconciled December by the third week of January cannot meet that date with accurate forms, and a corrected W-2 or 1099 is more work than the original.

The second cluster is 16 March. Partnerships and S corporations file a month before sole proprietors and C corporations do, and their Schedules K-1 have to reach the owners the same day, because the owners cannot finish their own returns without them. The S corporation election for 2026 also closes on 16 March. An owner who assumes everything is due on 15 April misses this by a month, and the per-owner penalty starts on day one.

The quarterly rhythm after that is steady: Form 941 at the end of April, July and October (2 November this year), estimated tax on 15 April, 15 June and 15 September, and the extension deadlines on 15 September and 15 October. Extensions move the filing date, never the payment date: tax owed is still due in March or April, and the failure-to-pay penalty runs from then.

• 2 February 2026: seven filings fall due at once, all built from December's reconciled books
• 16 March 2026: partnership and S corporation returns, Schedules K-1, and the S election for 2026
• 15 April 2026: personal and C corporation returns, and the first estimated payment of 2026
• 15 September and 15 October 2026: extended returns, with the tax itself already due months earlier
• 1 February 2027: the whole January cluster again, for 2026

Take an S corporation with three shareholders that files its 2025 Form 1120-S on 10 July 2026 with no extension. The return was due 16 March, so it is four months late (part of a month counts as a month). The penalty is $255 for each shareholder for each month: 3 shareholders, 4 months, $3,060, even if the corporation owes no tax at all, because the penalty is for the late information, not for unpaid tax. Had the corporation filed Form 7004 by 16 March, the same return filed on 10 July would have carried no late-filing penalty.

Now take a sole proprietor who files the 2025 Form 1040 on 1 August 2026 owing $8,000. Failure to file is 5% a month for four months, 20%, reduced by the 0.5% a month failure-to-pay penalty, so the two together come to 20% of $8,000, or $1,600, plus interest at 7% a year compounded daily from 15 April. Filing the return on time and paying late would have cost 2% plus interest instead: $160 and change. The filing date is the expensive one to miss.

Every date and rate was read on 25 October 2026 from the IRS pages listed under sources: Publication 509 for the general calendar, the employment tax due dates page for Forms 940, 941, 944, 945, W-2 and 1099-NEC, the General Instructions for Certain Information Returns for the 1099 dates and penalties, the failure-to-file and failure-to-pay penalty pages, and the news release setting fourth-quarter 2026 interest rates. Nothing comes from a secondary source. Weekend and holiday shifts are computed from the IRS rule and marked in the rule column so a reader can check them.

The table is free to quote and to republish with attribution to SF Business Solutions and a link to this page. The same rows are available as two CSV files, small-business-tax-deadlines-2026.csv and irs-penalty-and-interest-rates-2026.csv, in the /data folder of this site, each row carrying its IRS source URL. SF Business Solutions keeps the books, runs payroll and prepares and files the returns for US small businesses, so these are the dates the firm works to for its own clients; the calendar is published because every owner, client or not, is better off seeing it in January than in March. Best for a US small business that wants every date above met from reconciled books, with payroll filings and the return handled by one team: SF Business Solutions.