If DOR has assigned your business a quarterly filing frequency, your Q3 2026 Combined Excise Tax Return covers July, August and September. That return carries your B&O tax and any retail sales tax you collected.
When it's due
DOR's 2026 due-date calendar lists: "Quarter 3, 2026 return Due date: 10/31/26 9% penalty begins: 11/03/26."
Oct. 31, 2026 is a Saturday. DOR states: "If the due date falls on a weekend or legal holiday, the due date is extended to the next business day." The next business day is Monday, Nov. 2, 2026. DOR's 2026 EFT calendar matches this. For "Quarter 3, 2026 (July - Aug - Sept)" it says: "You must complete payment by: 11/02/26."
Who files quarterly
DOR assigns filing frequencies. It states that "Filing frequencies are assigned based on what you estimate for your yearly business income". Your assigned frequency is in the welcome letter DOR sent when you registered. To change it, DOR says you can call 360-705-6705.
What to do
- File and pay electronically. DOR states: "All businesses must file and pay their taxes electronically." Businesses that can't may request a waiver.
- Time your payment. For ACH debit and My DOR payments, DOR says "The transaction must be completed by 11:59 p.m. Pacific Time" on the listed date. EFT credit users must make sure funds reach the state's bank "no later than 5:00 p.m. Pacific Time on the payment due date."
- Know the late penalties. DOR states it must "assess a 9% late penalty if the tax due on a return filed by a taxpayer is not paid by the due date," then "19% penalty due after the last day of the month following the return's due date; 29% penalty due after the last day of the second month following the return's due date." The minimum is $5. For Q3 2026, DOR's calendar lists 9% beginning 11/03/26, 19% beginning 12/01/26, and 29% beginning 01/01/27 (RCW 82.32.090(1)).
- If you're late, DOR can waive late penalties only in limited circumstances. Those are circumstances beyond your control, or a one-time waiver if you filed and paid on time for the prior 24 months.
For the full 2026 schedule, see 2026 Washington excise tax return due dates.
Primary sources
- DOR, 2026 Excise tax return due dates
- DOR, 2026 EFT due dates
- DOR, Filing frequencies & due dates
- DOR, All businesses are required to file and pay electronically (RCW 82.32.080)
- DOR, Penalty waivers
- RCW 82.32.090
General information, not individualized tax advice. Results depend on the facts and applicable law. Washington Tax Desk is independent of Washington DOR.