Tax Deadlines for Q4 2026: Federal and Maryland Guide
The last quarter of the year is the busiest stretch on the tax calendar. October through December brings extended return deadlines, quarterly payroll filings, monthly sales tax returns, and a hard stop on December 31 for most year-end tax planning moves. It also overlaps with open enrollment for health coverage, which is a deadline that matters a great deal to self-employed business owners.
At Insightful Accounting Services, we help businesses throughout Columbia and Howard County close out the year cleanly so nothing slips through the cracks. Here's your complete Q4 deadline guide.
October 15 — The Big Extension Deadline
Extended 2025 Individual Returns (Form 1040) Due If you filed Form 4868 back in April, this is your final deadline to file your 2025 federal individual return. There are no further extensions. Missing this date triggers the failure-to-file penalty, calculated retroactively to April at 5% of the unpaid tax per month, up to 25%.
Extended 2025 Maryland Individual Returns (Form 502) Due Maryland grants an automatic six-month extension without requiring a separate form, which puts your extended state return due the same day. Remember that this was always an extension to file, not to pay and any 2025 balance has been accruing interest and the 0.5% monthly late-payment penalty since April 15. If you owe, making a partial payment now still reduces both.
Extended C-Corporation Returns (Form 1120) Due Calendar-year C-corporations that filed Form 7004 in April also face an October 15 federal deadline.
Maryland Employer Withholding — September Deposit Due Monthly Maryland withholding filers: your deposit for September wages is due October 15 on Form MW506.
Also due October 15: extended FBAR (FinCEN Form 114) filings and extended Form 3520 for foreign gifts and trusts. The Form 3520 penalty is severe (35% of the gross value of the transaction), so if this applies to you, do not let it slide.
October 20 — Maryland Sales & Use Tax
Maryland Sales and Use Tax Return — September / Q3 Due Maryland sales and use tax returns are due on the 20th of the month following the reporting period. Monthly filers owe their September return by October 20. Quarterly filers also file by October 20 for the Q3 period covering July, August, and September.
If you're not certain whether you're a monthly, quarterly, or annual filer, your frequency is assigned based on your average monthly sales tax liability. Give our office a call and we can confirm your status.
November 2 — Federal Payroll Tax Return (Form 941)
Federal Employer's Quarterly Tax Return — Q3 Due Employers must file IRS Form 941 for the third quarter (July through September). The usual October 31 deadline falls on a Saturday in 2026, so the filing date moves to Monday, November 2.
If you deposited all of your payroll taxes on time and in full throughout Q3, the IRS grants an automatic 10-day extension, moving your filing deadline to November 10. Most businesses should still aim for the November 2 date.
Payroll penalties remain the steepest the IRS imposes. Withheld employee taxes are trust fund money, and late deposits and late filings are treated accordingly. If payroll is handled in-house, this is the right moment to confirm your deposits and filings are aligned before year-end reconciliation.
Maryland Unemployment Insurance — Q3 Contribution Report Due Maryland's quarterly UI contribution and employment report is also due, moving from October 31 to the next business day.
November 16 — Maryland Corporate Extension Deadline
Extended Maryland Corporate Returns (Form 500) Due Here's a difference worth flagging: Maryland grants corporations a seven-month extension rather than the federal six. That puts extended Maryland corporate returns due November 15, which falls on a Sunday in 2026, so the deadline moves to Monday, November 16, a full month after the federal Form 1120 deadline.
Maryland Employer Withholding — October Deposit Due Monthly withholding filers: your October deposit shifts to November 16 for the same weekend reason.
November 20 — Maryland Sales & Use Tax (Monthly Filers)
Maryland Sales and Use Tax Return — October Due Monthly sales tax filers must file and remit their October return by November 20. Quarterly filers have no November obligation and your next return is due January 20, 2027 for Q4.
December 15 — Corporate Estimated Payments
Federal C-Corporation Estimated Tax — Q4 Installment Due C-corporations expecting to owe $500 or more in federal income tax must make the fourth and final 2026 installment by December 15, deposited via EFTPS. Note that this is a month earlier than the individual Q4 deadline — a distinction that catches business owners who mentally file both under "January."
Maryland Employer Withholding — November Deposit Due Monthly withholding filers: your November deposit is due December 15 on Form MW506.
December 21 — Maryland Sales & Use Tax (Monthly Filers)
Maryland Sales and Use Tax Return — November Due The usual 20th falls on a Sunday, so monthly filers have until Monday, December 21 to file and remit the November return.
December 31 — Year-End Cutoff
This is the hard stop for nearly every 2026 tax planning move. After this date, your options narrow to a handful of retirement contributions. Items to address before the calendar turns:
Required Minimum Distributions If you are 73 or older, your 2026 RMD must be taken by December 31. The penalty for a missed distribution is steep, and it is entirely avoidable.
Retirement Plan Deferrals Employee 401(k) deferrals must be made by year-end. Employer contributions and SEP-IRA funding generally have more runway, usually until your extended filing, deadline but deferrals do not.
Charitable Contributions Gifts must be completed by December 31 to count for 2026. For appreciated securities, start the transfer well before the last week of December; brokerages get slow and transfers occasionally don't settle in time.
Tax-Loss Harvesting Realize losses by year-end to offset 2026 gains, watching the 30-day wash sale window on either side of the sale.
Equipment and Fixed Assets Assets must be placed in service, not merely ordered or paid for, by December 31 to qualify for 2026 depreciation.
Entity Housekeeping Review reasonable compensation for S-corporation owners, settle any shareholder loan balances, and confirm accountable plan reimbursements are documented before the books close.
Health Insurance Open Enrollment — November 1 through January 15
For self-employed clients and small business owners buying their own coverage, this window is as much a Q4 deadline as anything else on this list.
Maryland runs its own exchange, Maryland Health Connection, so the dates aren't automatically the federal ones:
November 1, 2026 — Enrollment opens.
December 31, 2026 — Enroll by this date for coverage beginning January 1, 2027. Enrolling January 1 through 15 pushes your coverage to February 1.
January 15, 2027 — Open enrollment closes under the currently published schedule.
One caveat worth knowing. A 2025 federal rule would have shortened the enrollment window to end December 31, and Maryland Health Connection indicated in spring 2026 that it would follow that shorter schedule. A court vacated the rule in June 2026, and current listings put Maryland back from November 1 through January 15. Because this has moved more than once, treat December 31 as your working deadline, it's the date that governs January 1 coverage regardless of how the litigation ultimately resolves. Confirm at marylandhealthconnection.gov as November approaches.
Self-employed health insurance premiums are generally deductible above the line, so the plan you select here has a direct effect on your 2027 return. It's worth a conversation before you click enroll.
Looking Ahead — January 15, 2027
Q4 Estimated Tax Payments Due — Federal and Maryland Your fourth and final 2026 estimated payment covers September through December and is due January 15, 2027. Use IRS Form 1040-ES federally and Maryland Form 502D for the state.
The safe harbors are unchanged: pay at least 90% of your current-year liability, or at least 100% of last year's tax( 110% if your adjusted gross income exceeds $150,000). Maryland requires estimated payments once your expected liability exceeds $500 after withholding and credits.
One Maryland-specific option: in place of the January 15 installment, you may instead file your complete 2026 Maryland return and pay the full balance by January 31, 2027. For clients whose records close quickly, this can be a cleaner path.
Monthly Maryland withholding filers also have their December deposit due January 15.
Close the Year Strong — We're Right Here in Columbia
Q4 is the quarter where deadlines stack up and where good year-end planning actually changes what you owe. The difference between reacting in April and planning in November is often measured in real dollars.
Insightful Accounting Services works with businesses right here in Columbia, Maryland on payroll taxes, estimated payments, sales tax filings, and year-end planning, so you can focus on what you do best. Reach out before the December rush and let's build a plan.