Small Business Tax Calendar: Every Federal Deadline for Sole Proprietors, S-Corps, and Partnerships
Small business owners face multiple federal tax deadlines throughout the year. Missing a deadline triggers penalties, interest, and sometimes the loss of deduction opportunities. The deadlines vary by entity type (sole proprietor, S-Corp, partnership) and whether the business has employees.
January 15: Q4 estimated tax payment (individual/sole proprietor). Not required if filing the annual return and paying the balance by January 31.
January 31: W-2s due to employees. 1099-NEC due to contractors. Form 940 (annual FUTA) due. Form 941 (Q4 payroll) due.
February 28 / March 31: W-2 and 1099 copies due to the SSA/IRS (February 28 if paper, March 31 if electronic).
March 15: S-Corp return (Form 1120-S) due. Partnership return (Form 1065) due. S-Corp election (Form 2553) due for existing entities wanting S-Corp status for the current year.
April 15: Individual return (Form 1040) due, including Schedule C for sole proprietors. Q1 estimated tax payment due. Last day to make prior-year IRA contributions. Last day to make prior-year Solo 401(k) employee deferrals (if return isn’t extended).
June 15: Q2 estimated tax payment due.
September 15: Q3 estimated tax payment due. Extended S-Corp and partnership returns due. Extended Solo 401(k) and SEP IRA contribution deadline (if the individual return is also extended).
October 15: Extended individual return (Form 1040) due. Extended SEP IRA contribution deadline. Last day to establish and fund a SEP IRA for the prior year (for extended filers).
Monthly/quarterly throughout the year: Form 941 (quarterly payroll, due end of the month following each quarter). Payroll tax deposits (monthly or semi-weekly, depending on the deposit schedule).
What are the penalties for missing deadlines?
Late filing penalty: 5% of the unpaid tax per month, up to 25% maximum. If the return is more than 60 days late, the minimum penalty is $510 (2025) or 100% of the unpaid tax, whichever is less.
Late payment penalty: 0.5% of the unpaid tax per month, up to 25% maximum. This applies even if an extension was filed (the extension is to file, not to pay).
Estimated tax underpayment penalty: Calculated based on the IRS’s short-term interest rate, applied to the underpayment for each quarter. Not a fixed percentage. Can be avoided entirely by meeting the prior-year safe harbor (100%/110% of last year’s tax).
Payroll tax penalties (Form 941): The Trust Fund Recovery Penalty (TFRP) under IRC 6672 is 100% of the unpaid trust fund taxes (employee withholding and the employee share of FICA). This penalty is assessed personally against the “responsible person” (typically the business owner) and can’t be discharged in bankruptcy.
1099/W-2 late filing: $60 per form if filed within 30 days of the deadline. $130 if filed by August 1. $330 if filed after August 1 or not filed. Maximum penalties vary by business size.
What deadlines do extension filers need to watch?
Filing an extension extends the filing deadline but NOT the payment deadline. The key dates for extended filers:
- April 15: The tax payment is still due. Estimate the liability and pay with the extension (Form 4868 for individuals, Form 7004 for S-Corps and partnerships). Underpayment accrues interest and late-payment penalties from April 15.
- September 15: Extended S-Corp (Form 1120-S) and partnership (Form 1065) returns are due. Extended Solo 401(k) employer contributions and SEP IRA contributions are due (if the individual return is also extended to October 15).
- October 15: Extended individual returns (Form 1040) are due. This is the absolute last day for SEP IRA establishment and contribution for the prior tax year.
Can I adjust my estimated tax payments mid-year if my income changes?
Yes. Estimated taxes are not locked in after the first quarter. If your income increases or decreases significantly, you can recalculate and adjust future quarterly payments. The annualized income installment method (Form 2210, Schedule AI) lets you base each quarter’s payment on income actually earned through that period rather than dividing the annual estimate by four. This is particularly useful for seasonal businesses where income concentrates in certain months. Recalculate after each quarter closes and adjust the next payment to stay on track with either the current-year or safe harbor target.
What are the penalties for misclassifying employees as independent contractors?
The penalties are substantial and compound across multiple agencies. The IRS can assess the employer’s share of FICA (7.65% of wages), plus penalties of 1.5% of wages for failure to withhold income tax and 20% of the employee’s share of FICA. These penalties increase to 3% and 40% respectively if the misclassification is deemed intentional (no 1099s filed). State penalties add unemployment tax, workers’ compensation premiums that should have been paid (often with interest and penalties), and potential fines per misclassified worker. Misclassified workers can also claim overtime, minimum wage, benefits, and other protections they were denied under employment law. The IRS Voluntary Classification Settlement Program (VCSP) offers reduced penalties if you come forward before an audit.
Related guides:
- Small Business Tax Calendar 2025: Every Filing Deadline
- Small Business Tax Calendar 2025: Every Deadline for Estimated Taxes, Payroll, and Filing
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Yarik Yarosh, CPA. "Small Business Tax Calendar: Every Federal Deadline for Sole Proprietors, S-Corps, and Partnerships." Blue Cloud CPA, September 5, 2026. https://bluecloudcpa.com/guides/small-business-tax-calendar-deadlines
This guide is general information, not tax advice for your specific situation. Which points apply, and how, depends on your facts.