Washington sales tax filing: due dates, excise return, penalties

One return carries two taxes

Washington collects retail sales tax and B&O tax on the same excise tax return, filed in My DOR, the state's online account system. For a bookkeeper, the client's sales tax liability account and the B&O expense account both come out of one filing.

The state rate is 6.5%. Local city and county rates are added on top, and the combined rate depends on where the customer receives the goods or service. DOR calls this destination-based and publishes a Tax Rate Lookup Tool that searches by address or ZIP+4. A seller that ships across the state needs the rate by delivery address, not by the seller's location.

Collected sales tax is held in trust for the state. If the client spent it, the liability is still due. DOR's extension page lists lack of funds and poor cash flow as reasons that do not qualify.

How DOR assigns monthly, quarterly or annual

DOR assigns frequency at registration from the client's estimated tax liability: annual at $1,050 or less, quarterly from $1,051 to $4,800, monthly at $4,801 or more. DOR's page also lists estimated annual income bands it uses at assignment: annual from $0 to $60,000 of Washington income for most retail, service, manufacturing and wholesale businesses, and monthly at $60,000 and up for construction and restaurants.

Those bands describe the starting estimate and overlap at the edges, so read the frequency off the client's My DOR account instead of computing it. If a new client's first year runs well above the estimate, compare the filed liability to the bands after two quarters.

Due dates and penalty start dates for 2026 periods

Monthly returns are due on the 25th of the following month, quarterly returns on the last day of the month after the quarter ends, and annual returns on April 15 of the following year. For 2026 periods, the October return is due November 25, the November return December 25 and the December return January 25, 2027. Quarterly dates are April 30, July 31, October 31 and January 31, 2027. The annual 2026 return is due April 15, 2027.

DOR's rule is that a due date on a weekend or legal holiday moves to the next business day. October 31, 2026 was a Saturday, so Quarter 3 was due Monday, November 2, and DOR's table lists the 9% penalty as beginning November 3. December 25 is a Friday and a legal holiday, so the November monthly return rolls to Monday, December 28, and the 9% penalty begins the day after. January 31, 2027 is a Sunday, so Quarter 4 rolls to Monday, February 1, with the 9% penalty beginning February 2.

For Quarter 3, DOR lists 19% from December 1 and 29% from January 1, 2027. For the November monthly return, 19% starts February 2, 2027 and 29% starts March 2, 2027. For Quarter 4, 19% starts March 2 and 29% starts April 1. Copy these from DOR's 2026 table instead of counting.

Today is November 9, 2026. A quarterly client that has not filed Quarter 3 is already in the 9% tier, and the 19% tier begins December 1. Also change lastReviewed and the 'as of' dates to 2026-11-09. File now and request the waiver on the return.

Penalties, interest and the waiver rule

DOR states the penalty as 9% of the tax if unpaid at the due date, 19% if still unpaid after the last day of the month following the due date, and 29% after the last day of the second following month. The minimum is $5. Each tier is worded as a percentage of the tax due, so I read the tiers as replacing each other, not adding up. Confirm against the assessment notice if one arrives.

Worked example: a quarterly client owes $2,000 for Quarter 3. Paid before December 1, the penalty is 9% of $2,000, or $180. Paid in December, it is 19% of the same $2,000. Paid after December 31, it is 29%. Interest is separate: DOR's table lists 6% for 2026 on both assessments and refunds, and the rate changes every year.

A waiver is available two ways. Circumstances beyond the client's control qualify under WAC 458-20-228, but lack of funds and not knowing taxes were due generally do not. First-time relief applies when the client filed and paid every required return on time for the 24 months before the late period, and it covers only one return in 24 months. When filing electronically, check the waiver box on the return.

The B&O layer and the small business credit

B&O is a gross receipts tax, so it applies to revenue before expenses and is owed even without profit. On DOR's classifications page as of November 10, 2026, retailing is 0.471%, wholesaling is 0.484%, and service and other activities are 1.5% when prior-year receipts were under $1,000,000, 1.75% from $1,000,000 to $4,999,999 and 2.1% at $5 million or more. The page shows no effective date, so confirm the rates against what the return calculates when filing a different period.

Worked example: a retailer with $80,000 of taxable retail sales in a quarter owes $5,200 of state sales tax at 6.5%, before local rates, plus retailing B&O at 0.471% of the same $80,000. A retailer with a service line must split receipts by classification. DOR lists more than 50, and a wrong classification is the usual reason a return is wrong while the sales tax figure is right.

The Small Business B&O Tax Credit, under WAC 458-20-104, applies when total B&O due is under a threshold by filing frequency. Credit 720 applies when 50% or more of taxable income is service and other activities, gambling contests of chance, for profit hospitals, scientific R&D or real estate commissions. For periods beginning on or after January 1, 2023, the thresholds are $320 monthly, $960 quarterly and $3,840 annual. Credit 815 covers everyone else: $110 monthly, $330 quarterly and $1,320 annual. Electronic filers have it calculated automatically.

Out-of-state sellers and marketplaces

A client with no Washington presence must collect sales tax when it has more than $100,000 of combined gross receipts sourced to Washington. Collection starts the first day of the month that begins at least 30 days after crossing. DOR's example: crossing on October 15 means collecting from December 1.

For a client selling through a marketplace, the seller is not required to collect on facilitated sales if it has documentation that the facilitator is collecting and reporting the tax. Keep that documentation in the file with the facilitator's name and period.

Records to collect each period

Collect the sales report by delivery location, gross sales for the period, non-taxable sales with a reason for each, exemption certificates received, and refunds pulled separately from the point-of-sale export.

For a monthly client, send this on the 10th: "For the October return, please send the sales export with delivery ZIP for each order, a list of any sale you did not charge tax on and why, and any resale certificates you received this month. Please send it by the 18th so we can file before the 25th." That leaves a week.

Reconcile the sales tax payable account to the return before filing. A balance left afterward usually means tax at the wrong local rate or an exempt sale booked as taxable.

Running the cycle with a recurring request

With ten Washington clients on mixed frequencies, you need a due-date calendar and one repeating request per client. In Usual, a recurring request can hold a table field for non-taxable sales with reasons and a file upload for the sales export, and reminders follow the due date. This page reflects DOR's rate and due-date pages on November 10, 2026, so check DOR's tax change notices before the first 2027 filing.