Business Owner Tax Deadlines 2026: Complete Calendar
Missing a tax deadline costs money — estimated tax penalties, retirement plan disqualification, lost deductions. This calendar covers every IRS filing deadline, quarterly payment date, retirement plan contribution window, and year-end planning action relevant to business owners in 2026. Dates verified against IRS Publication 509, IRS Notice 2025-67, and current DOL/PBGC guidance.
How to use this guide: Jump to the upcoming date range most relevant to you. Dates already past are noted — they're still useful for extension planning. Retirement plan deadlines are listed separately after the main calendar because they depend on your plan type, not just the calendar.
2026 business tax calendar by date
January 2026 (passed)
Date
Deadline
Who
Jan 15
Q4 2025 estimated tax payment
Sole proprietors, S-corp shareholders, partners (skip if filing/paying full tax by Jan 31)
Jan 31
Furnish W-2s to employees; Form 1099-NEC to contractors; file W-2s with SSA and 1099s with IRS
All employers; businesses paying $600+ to non-employee contractors
Jan 31
Form 941 (Q4 2025 payroll taxes)
Employers with quarterly payroll tax deposits
Jan 31
SIMPLE IRA — employee salary deferrals from December must be deposited
SIMPLE IRA plan sponsors (within 30 days of month-end)
March 2026 (passed)
Date
Deadline
Who
Mar 16
S-corp (Form 1120-S) and partnership (Form 1065) returns due — or file Form 7004 for 6-month extension to September 151
S-corporations, multi-member LLCs taxed as partnerships
Mar 16
Schedule K-1s due to shareholders/partners
S-corps and partnerships (extension of entity return extends K-1s too)
April 2026 (passed)
Date
Deadline
Who
Apr 15
Individual return (Form 1040) — or file Form 4868 for 6-month extension to October 15
Sole proprietors, S-corp shareholders, partners reporting K-1 income
Apr 15
C-corp return (Form 1120) — or Form 7004 for 6-month extension to October 15
C-corporations (calendar year)
Apr 15
Q1 2026 estimated tax payment
Sole proprietors, S-corp shareholders, partners, C-corps (if using estimated taxes)
Traditional/Roth IRA contribution deadline for 2025 tax year
All individuals with earned income
June 2026 (passed)
Date
Deadline
Who
Jun 15
Q2 2026 estimated tax payment
Sole proprietors, S-corp shareholders, partners; C-corps (2nd installment)
July 2026 — coming up
Date
Deadline
Who
Jul 31
Form 5500 / 5500-EZ due for calendar-year retirement plans — or file Form 5558 by July 31 to extend to October 152
Any plan that filed a Form 5500 last year: 401(k), profit sharing, defined benefit, cash balance plans; Form 5500-EZ for solo 401k plans with assets over $250K
Jul 31
Form 941 (Q2 2026 payroll taxes)
Employers
Form 5500 note for solo 401(k) owners: If your solo 401(k) had total assets exceeding $250,000 at the end of the 2025 plan year, you must file Form 5500-EZ by July 31, 2026. Below $250K, no filing required. Many solo 401k owners miss this and face steep penalties ($250/day, up to $150,000).
September 2026
Date
Deadline
Who
Sep 15
Q3 2026 estimated tax payment
Sole proprietors, S-corp shareholders, partners; C-corps (3rd installment)
Sep 15
Extended S-corp (Form 1120-S) and partnership (Form 1065) returns due1
S-corps and partnerships that filed Form 7004 in March
Sep 15
Schedule K-1s due to shareholders/partners (if S-corp/partnership filed extension)
S-corps and partnerships on extension
October 2026
Date
Deadline
Who
Oct 1
SIMPLE IRA new plan establishment deadline — last day to adopt a SIMPLE IRA for 2026 tax year contributions3
Business owners with 1–100 employees who want to add a SIMPLE IRA for 2026. No extensions. Miss this and you must wait until 2027.
Oct 15
Extended individual return (Form 1040) due
Individuals who filed Form 4868 in April
Oct 15
Extended C-corp return (Form 1120) due
C-corps that filed Form 7004 in April
Oct 15
SEP-IRA contribution deadline with extension — if you filed a personal return extension, you have until October 15 to contribute for 2025 (sole props) or 2026 (depends on entity year)4
Self-employed individuals and S-corp owners with individual filing extensions
Oct 15
Form 5500 / 5500-EZ extended deadline
Plans that filed Form 5558 by July 31
Oct 31
Form 941 (Q3 2026 payroll taxes)
Employers
November 2026
Date
Deadline
Who
Nov/Dec
PTET election deadlines (varies by state) — most states require the election by December 31; some require it by November 15 or earlier5
S-corps and partnerships in states with pass-through entity tax elections; especially valuable under 2026 OBBBA $40,400 SALT cap
December 2026 — year-end planning window
December 31 is the hard cutoff for a surprising number of valuable elections and actions. Many of these cannot be done retroactively in January — the opportunity closes at midnight December 31.
By Dec 31
Action
Details
Roth conversions
Convert traditional IRA or 401(k) funds to Roth
Conversions must complete in 2026 to count for the 2026 tax year. Especially powerful for business owners in lower-income years or post-sale before income rises. See Roth Conversion Guide.
New retirement plan adoption
Establish a new 401(k), profit sharing, defined benefit, or cash balance plan
Most plans must be adopted by December 31 to allow employee deferrals for 2026. Solo 401(k) for sole proprietors: SECURE 2.0 §317 allows adoption as late as your April 15, 2027 filing deadline. See Solo 401(k) Guide.6
§179 / bonus depreciation
Place qualifying property in service
Equipment, machinery, and other qualifying assets must be placed in service by December 31 to claim the 2026 deduction. OBBBA restored 100% bonus depreciation permanently for property acquired after January 19, 2025. See Section 179 & Bonus Depreciation Guide.
Solo 401(k) employee deferrals
Last day to make employee elective deferrals to an existing solo 401(k)
For entities other than sole proprietors, salary deferrals must be designated and deposited by December 31. The SECURE 2.0 sole proprietor exception only covers new plan adoption; payroll deferrals still have an earlier deadline tied to compensation paid.7
S-corp reasonable compensation
Run final payroll; ensure W-2 is at or above defensible salary
W-2 wages that support Solo 401(k) employer contributions, QBI deduction, and §162(l) health insurance deduction must appear on the 2026 W-2. Final payroll must be run before December 31. See Reasonable Compensation Guide.
PTET election
Make the pass-through entity tax election for 2026
Many states require the election by December 31 (some by November). Election enables the business to deduct state income taxes at the entity level, bypassing the $40,400 individual SALT cap under OBBBA. See PTET Calculator.
Charitable contributions
Make gifts, fund a donor-advised fund (DAF), or transfer assets to a CRT
Charitable deductions are claimed in the year the contribution is made. A cash gift to a DAF by December 31 locks in the 2026 deduction even if grants are made later. See CRT Guide.
Augusta Rule rental
Schedule and hold home office rental meetings
§280A(g) exclusion requires up to 14 rental days per year; the rental must actually occur. Can't back-date into 2027. See Augusta Rule Guide.
Tax-loss harvesting
Sell underperforming positions to realize losses
Losses must be realized in 2026 to offset 2026 gains. Wash-sale rule (30 days before/after) applies to substantially identical securities.
Retirement plan contribution deadlines by plan type
Retirement plan contribution deadlines are separate from filing deadlines and vary significantly by plan type. Getting these wrong means losing the deduction.
Plan
Employee deferral deadline
Employer contribution deadline
New plan setup deadline
Solo 401(k)
Dec 31, 2026 (most entities); Apr 15, 2027 for sole props under SECURE 2.0 §317
Business tax return + extensions (e.g., Oct 15, 2027 for sole props with extension)
Dec 31, 2026 (most); Apr 15, 2027 for sole props
SEP-IRA
N/A (employer-only contributions)
Tax return + extensions (Apr 15 or Oct 15, 2027)
Tax return + extensions — can open and fund same day as filing
SIMPLE IRA
Within 30 days of each payroll period
Tax return + extensions
Oct 1, 2026 to start for 2026 plan year
Traditional 401(k)
Dec 31, 2026
Tax return + extensions
Dec 31, 2026
Safe Harbor 401(k)
Dec 31, 2026
Tax return + extensions
Oct 1, 2026 for new plan; Dec 1 to add SH feature to existing plan
Cash Balance / Defined Benefit
N/A
Actuarially determined; typically by 8.5 months after plan year end (Sep 15 for calendar-year plans), with extensions. Minimum required contributions may vary.
If you're reading this in summer 2026, the most time-sensitive items are:
Form 5500 / 5500-EZ by July 31. If your solo 401(k) or profit-sharing plan has assets over $250K, this is due July 31 or you must file Form 5558 to extend. Easy to overlook and expensive to miss.
Q3 estimated taxes by September 15. Use the Quarterly Tax Calculator to verify you're meeting the safe harbor threshold (100% of prior year tax, or 110% if prior-year AGI exceeded $150K).
New SIMPLE IRA by October 1. If you want to add a SIMPLE IRA for employees before year-end, October 1 is the hard deadline. After that, it's a 2027 decision.
S-corp extended return by September 15. If you're on extension, the return and final K-1s are due September 15. Missing the extended deadline means the extension was never granted — the original March 16 deadline governs, and you're already late.
Year-end plan adoption. If you're considering a cash balance plan, defined benefit plan, or traditional 401(k) for the first time, the plan must typically be in place by December 31. Cash balance actuarial setup takes 4–8 weeks. Start the conversation in October to give your plan administrator and advisor time to execute.
Early 2027 deadlines (for 2026 tax year)
Date
Deadline
Notes
Jan 15, 2027
Q4 2026 estimated tax payment
Or skip if filing and paying in full by Jan 31
Jan 31, 2027
W-2s to employees; 1099-NEC to contractors; file with IRS/SSA
Standard employer obligation
Apr 15, 2027
Individual return or extension; SEP-IRA contribution without extension; IRA/Roth IRA contributions for 2026 tax year; sole-proprietor solo 401(k) plan adoption and employee deferrals (SECURE 2.0 §317)
Busiest single deadline of the year
Oct 15, 2027
Extended individual return; SEP-IRA contribution with extension; solo 401(k) employer contributions (sole proprietors with extended return)
Final backstop for most retirement plan contributions
Make the most of your 2026 planning window
A fee-only financial advisor who works with business owners can map these deadlines against your specific situation — identifying whether a cash balance plan, PTET election, or year-end Roth conversion would move the needle, and coordinating timing with your CPA so nothing falls through the cracks.
Fee-only · No commissions · Free match · No obligation
IRS Publication 509 (2026): Tax Calendars — authoritative IRS calendar covering all business entity filing deadlines; March 16 S-corp/partnership original deadline confirmed (March 15 falls on Sunday); September 15 extended S-corp/partnership deadline; April 15 individual/C-corp deadlines.
IRS Form 5500 Corner — Form 5500 / 5500-EZ due the last day of the 7th month after plan year ends (July 31 for calendar-year plans); Form 5558 extends by 2.5 months to October 15; $250,000 threshold for solo 401(k) / Form 5500-EZ requirement; penalty $250/day up to $150,000.
IRS: SIMPLE IRA Plan FAQs — October 1 hard deadline to establish a new SIMPLE IRA for the current plan year; no extensions available; must notify employees at least 60 days before plan effective date.
IRS: SEP Plan FAQs — SEP-IRA can be established and funded up to the tax return due date plus extensions (October 15 for individuals who filed Form 4868); contribution must be made to existing SEP or new SEP by that date.
IRS: Pass-Through Entity Tax Overview — state PTET election availability and general federal treatment; 2026 SALT cap of $40,400 under OBBBA; election timing varies by state, typically by December 31 of the tax year or an earlier state-set deadline.
IRS: SECURE 2.0 Act Overview — §317 allows sole proprietors with no common-law employees to adopt a Solo 401(k) and make elective-deferral contributions as late as their individual return due date (April 15, 2027, or October 15 with extension); employer profit-sharing contributions still due by return + extension.
IRS: 401(k) Plan Overview — employee salary deferrals to 401(k) plans (including Solo 401(k)) must be designated before the compensation is earned and deposited according to plan terms; for most entities December 31 is the effective cutoff for 2026 deferrals; 2026 contribution limit: $24,500 employee deferral + employer contributions up to $72,000 total (IRS Notice 2025-67).
Filing dates verified as of June 2026 against IRS Publication 509 and applicable DOL guidance. State PTET deadlines vary — confirm with your state tax authority. Consult a qualified CPA or tax attorney for advice specific to your situation.