Q3 Tax & Business Deadlines Every Maryland Business Owner Needs to Know
Summer may feel like a slower season, but the July through September stretch is anything but quiet on the tax calendar. Q3 brings a fresh set of federal and Maryland state deadlines that business owners need to stay on top of — from payroll tax filings to estimated payments and monthly sales tax returns. Missing these can lead to penalties and interest that eat into your bottom line.
At Insightful Accounting Services, we help businesses throughout Columbia and Howard County navigate these mid-year obligations so nothing slips through the cracks. Here's your complete Q3 deadline guide.
July 15 — Maryland Withholding Tax (Monthly Filers)
Maryland Employer Withholding — June Deposit Due If you are a monthly filer for Maryland employer withholding taxes, your deposit for June wages is due on July 15. File using Maryland Form MW506 and ensure the amount remitted matches the Maryland income tax withheld from your employees' paychecks during June.
Staying current on monthly withholding deposits is one of the most important compliance habits a business can maintain. The Maryland Comptroller's office assesses penalties and interest for late or underpaid deposits.
July 20 — Maryland Sales & Use Tax
Maryland Sales and Use Tax Return — June / Q2 Due Maryland sales and use tax returns are due on the 20th of the month following the reporting period. For monthly filers, the June return is due July 20. For quarterly filers, your Q2 return (covering April, May, and June) is also due on July 20.
This is a commonly overlooked deadline because it falls in the middle of summer. If you collect sales tax from customers in Maryland, make sure you're tracking your filing frequency (monthly, quarterly, or annual) and remitting what's owed on time. Not sure of your filing frequency? It's based on your average monthly sales tax liability. Give our office a call and we can confirm your status.
July 31 — Federal Payroll Tax Return (Form 941)
Federal Employer's Quarterly Tax Return — Q2 Due Employers must file IRS Form 941 — the Employer's Quarterly Federal Tax Return — by July 31 for the second quarter (April through June). This form reports wages paid, federal income tax withheld, and Social Security and Medicare taxes for all employees during Q2.
If you deposited all of your payroll taxes on time and in full throughout Q2, the IRS grants an automatic 10-day extension, moving your filing deadline to August 10. However, most businesses should aim to file by July 31 to stay safe.
Payroll tax penalties are among the steepest the IRS imposes — starting at 5% of the unpaid tax per month, up to 25%. The IRS treats withheld employee taxes as trust fund money, so late deposits and late filings are taken seriously. If your payroll is handled in-house, double-check that your deposits and filings are aligned.
August 15 — Maryland Withholding Tax (Monthly Filers)
Maryland Employer Withholding — July Deposit Due Monthly withholding filers: your Maryland income tax deposit for July wages is due on August 15, filed on Form MW506.
This is also a good mid-summer checkpoint to review your payroll records and make sure your year-to-date withholding deposits are accurate and reconciled.
August 20 — Maryland Sales & Use Tax (Monthly Filers)
Maryland Sales and Use Tax Return — July Due Monthly sales tax filers must file and remit their July sales and use tax return by August 20. Quarterly filers do not have a filing due in August — your next return will be due October 20 for Q3.
September 15 — The Biggest Q3 Deadline
Federal Estimated Tax Payments — Q3 This is the most significant Q3 deadline for self-employed individuals, business owners, and anyone with income not subject to withholding. Your third estimated tax payment for 2025 — covering June through August — is due September 15. Use IRS Form 1040-ES to calculate and submit your payment.
Missing this payment, or underpaying, can result in an IRS underpayment penalty that accrues from the due date until you pay. To avoid this penalty, you can meet any one of the IRS safe harbors:
Pay at least 90% of your current-year tax liability, or
Pay at least 100% of last year's tax (110% if your adjusted gross income exceeded $150,000)
Maryland also requires quarterly estimated payments from individuals and businesses. Maryland's Q3 estimated payment is likewise due September 15, filed using Form 502D (individuals) or the appropriate corporate estimated payment form. Maryland's threshold for required estimated payments is $500 or more in expected tax liability.
Federal Corporate Estimated Tax Payments C-corporations that expect to owe $500 or more in federal income taxes must also make quarterly estimated payments. The Q3 installment (the third of four payments) is due September 15 using IRS Form 1120-W as a worksheet and deposited via EFTPS.
Maryland Withholding Tax — Monthly Filers Monthly withholding filers: your August withholding deposit is due September 15.
September 20 — Maryland Sales & Use Tax (Monthly Filers)
Maryland Sales and Use Tax Return — August Due Monthly sales tax filers must file their August sales and use tax return by September 20. As a reminder, quarterly filers are not due again until October 20 for the Q3 period (July–September).
Stay Ahead — We're Right Here in Columbia
Managing quarterly deadlines on top of running your business is a lot. The good news is you don't have to track all of this on your own. Insightful Accounting Services works with businesses right here in Columbia, Maryland to handle payroll taxes, estimated payments, sales tax filings, and everything in between — so you can focus on what you do best.