Q4 is the fourth quarter of the year. For anyone on a calendar year — which covers most individuals and businesses — Q4 runs from October 1 through December 31. Those three months carry a heavy concentration of tax deadlines, payroll obligations, and last-chance planning moves that determine what you owe when you file in the spring.
What Q4 Covers
On a calendar year, the four quarters split cleanly: January through March, April through June, July through September, and October through December. Q4 is the final stretch, and it aligns with the way most federal filing deadlines are written.
A business can pick a different twelve-month cycle, called a fiscal year, under the Internal Revenue Code. A fiscal year ends on the last day of any month other than December, or it can follow a 52-to-53-week period the taxpayer elects.1Office of the Law Revision Counsel. 26 U.S.C. 441 – Period for Computation of Taxable Income If a company’s fiscal year ends June 30, its Q4 is April through June. Some retailers end their fiscal year in January or February so a single Q4 captures the full holiday selling season and the returns that follow.
If you keep no books or have no regular accounting period, the IRS defaults you to the calendar year.1Office of the Law Revision Counsel. 26 U.S.C. 441 – Period for Computation of Taxable Income Switching from one fiscal year to another creates a short tax year — a return that covers fewer than twelve months. Sole proprietors file the short-year return by the 15th day of the fourth month after the short year ends; partnerships and S corporations file by the 15th day of the third month.2Internal Revenue Service. Starting or Ending a Business
Q4 Estimated Tax Payments
If part of your income isn’t subject to withholding — self-employment earnings, investment gains, rental income — you probably pay estimated taxes four times a year. The fourth installment covers income earned September 1 through December 31, and it’s due January 15 of the following year.3Internal Revenue Service. Estimated Tax When January 15 falls on a weekend or federal holiday, the deadline moves to the next business day.
There’s a shortcut. You can skip the January 15 payment if you file your full return and pay any remaining balance by January 31. That works when your income records are already in hand and you’re ready to file early.
Calendar-year corporations run on a different schedule. Their fourth estimated installment is due December 15, before the quarter even ends, rather than in January. Underpaying any installment can trigger penalties that accrue interest back to the original due date, so businesses with uneven income should refresh their projections before each deadline arrives.
Year-End Payroll and Contractor Filings
Q4 sets off a chain of employer deadlines that carry into late January and beyond. The penalties for filing information returns late or with errors escalate the longer you wait, and they apply separately to the return you file with the IRS and the statement you furnish to the worker.4Internal Revenue Service. Information Return Penalties For a business with dozens of employees, a short delay can add up fast.
W-2s and 1099-NECs
Every employer who withholds income or employment taxes must furnish each employee a W-2 by January 31 of the following year, showing total wages, federal income tax withheld, and Social Security and Medicare wages and taxes.5Office of the Law Revision Counsel. 26 U.S.C. 6051 – Receipts for Employees If an employee leaves before December 31 and asks for the W-2 early, the employer has 30 days from the request to provide it, though no earlier than the end of the calendar year for final wage calculations.6eCFR. 26 CFR 31.6051-1 – Statements for Employees
Businesses that paid an independent contractor $600 or more during the year must issue a 1099-NEC, also due to recipients by January 31. Verify taxpayer identification numbers and current addresses before the year ends to avoid corrections.
Form 941
Employers who pay wages subject to employment taxes file Form 941 each quarter. The Q4 filing is due January 31.7Internal Revenue Service. Employment Tax Due Dates The form reports total wages, income tax withheld, and both the employer’s and employees’ shares of Social Security and Medicare taxes. Deposit all employment taxes on time throughout the quarter and you get an automatic ten-day extension, to February 10.
ACA Reporting
Employers with 50 or more full-time employees — applicable large employers — must report the health coverage they offered. For the 2025 calendar year, the deadline to furnish Form 1095-C to each full-time employee is extended to March 2, 2026. Forms 1094-C and 1095-C go to the IRS by the same date on paper, or by March 31, 2026, electronically.8Internal Revenue Service. Instructions for Forms 1094-C and 1095-C
Year-End Tax Moves Before December 31
Q4 is the last window to take actions that lower your current-year tax bill. Three matter most.
Section 179
Rather than depreciating equipment over several years, qualifying businesses can deduct the full cost of eligible assets in the year they’re placed in service. For tax years beginning in 2026, the maximum Section 179 deduction is $2,560,000, and it starts phasing out once total qualifying property placed in service exceeds $4,090,000. The asset has to be purchased and put to use by December 31 — or by the end of your fiscal year — to count.
Bonus Depreciation
Bonus depreciation had been phasing down, dropping to 60% for 2024 and 40% for 2025, but the One Big Beautiful Bill Act permanently restored 100% bonus depreciation for qualified property acquired after January 19, 2025.9Internal Revenue Service. Notice 2026-11 – Interim Guidance on Additional First Year Depreciation Deduction A business that buys qualifying equipment during Q4 of 2026 can deduct the entire cost in the first year. Unlike Section 179, bonus depreciation has no dollar cap and isn’t limited to net income, though it can create or increase a net operating loss.
Charitable Contributions
For a donation to count toward the current year, the payment has to be made within the taxable year.10Office of the Law Revision Counsel. 26 U.S. Code 170 – Charitable, Etc., Contributions and Gifts If you mail a check on December 31, the postmark date generally controls, not when the charity deposits it. Credit card charges count in the year the charge is made. Contributions of property worth more than $5,000 (other than publicly traded stock) require a qualified appraisal, so start the paperwork early enough to finish before the year closes.
Q4 for Public Companies
Publicly traded companies file periodic reports with the SEC. The first three quarters each require a Form 10-Q, but the end of Q4 triggers something larger: the Form 10-K, which covers the entire fiscal year rather than a single quarter.11Office of the Law Revision Counsel. 15 U.S.C. 78m – Periodical and Other Reports
Large accelerated filers file the 10-K within 60 days after fiscal year-end. Accelerated filers get 75 days. All other filers get 90. The 10-K requires consolidated balance sheets and income statements presenting a unified picture of the year’s financial performance, certified by independent public accountants.12U.S. Securities and Exchange Commission. Form 10-K Missing the deadline can lead to SEC enforcement actions, civil penalties, and potential delisting. Knowingly certifying a financial report that doesn’t meet legal requirements exposes corporate officers to criminal fines and imprisonment under the Sarbanes-Oxley Act.13Office of the Law Revision Counsel. 18 U.S. Code 1350 – Failure of Corporate Officers to Certify Financial Reports
Closing the Books Internally
Beyond tax filings and SEC reports, Q4 is when internal operations turn toward closing the year. Financial teams reconcile every account so internal records match bank statements, vendor invoices, and other third-party data. Companies that file public reports or that have lenders requiring audited financials bring in external auditors during this period to verify that the numbers are free from material errors.
Businesses that produce, buy, or sell merchandise generally need beginning-of-year and end-of-year inventory figures to calculate taxable income accurately. For many companies the Q4 physical count is the foundation of the cost-of-goods-sold figure on the tax return. Small business taxpayers using a simplified inventory method under Section 471(c) who take physical counts as part of regular practice must use those counts in their books and records.14eCFR. 26 CFR 1.471-1 – Need for Inventories Scheduling the count close to the last day of your fiscal year minimizes adjustments for goods received or shipped between the count and year-end.
Finally, teams compare actual revenue and spending against the budgets set at the start of the year. Variance analyses show where the business overspent, underspent, or missed revenue targets, and they feed directly into next year’s budget before the new fiscal year begins.