Washington has no personal or corporate income tax, but that does not mean no filing obligations. CPAs must handle the Business & Occupation (B&O) tax, the state’s capital gains tax, and one of the country’s steepest estate taxes — the latter two frequently overlooked because they aren’t “income tax.”
Washington Tax Deadlines at a Glance (2026)
Filing | Frequency / Due Date |
|---|---|
B&O — monthly filers | 25th of the following month |
B&O — quarterly filers | Apr 30 / Jul 31 / Oct 31 / Jan 31 |
B&O — annual filers | April 15 |
Capital gains tax (2025) | May 1, 2026 (extended) |
Estate tax | 9 months after date of death |
The Department of Revenue assigns B&O filing frequency by business size. Note that annual filers are due April 15, not the quarterly dates — a common mix-up. Retail sales and use tax are reported on the same Combined Excise Tax Return and schedule.
The B&O Tax
The B&O tax applies to gross receipts with no deduction for costs, so it is owed even at a loss. Rates vary by classification: retailing 0.471%, wholesaling and manufacturing 0.484%, and service & other activities on a tiered schedule — 1.5% under $1M in prior-year revenue, 1.75% from $1M–$5M, and 2.1% at $5M and above. Late-filing penalties escalate to 9%, 19%, then 29%.
Capital Gains Tax (Often Missed)
Since 2022 (upheld in 2023), Washington taxes long-term capital gains above a standard deduction ($278,000 for 2025). Effective 2025, the rate is now tiered: 7% on gains up to $1 million and 9.9% above $1 million. The 2025 return is normally due April 15, 2026, but the Department of Revenue extended the 2025 deadline to May 1, 2026. This applies wherever there is a Washington long-term capital gains obligation — a real trap for clients selling businesses or investments.
Estate Tax (Among the Highest)
Washington’s estate tax exemption was substantially raised in 2025: $3,076,000 for deaths in the first half of 2026 and $3,000,000 thereafter — up from the old $2,193,000 that expired mid-2025. Rates are steep and temporarily higher: 10% to 35% for deaths through June 30, 2026, then 10% to 20%. The estate tax return and payment are due nine months after the date of death.
CPA Action Steps
Match the B&O due date to the client’s assigned frequency (annual = April 15)
Screen every high-income client for the tiered capital gains tax — 2025 due May 1, 2026
Update estate planning for the ~$3M exemption and 35% top rate
Remember B&O is owed on gross receipts even in a loss year
Verify current rates, thresholds, and dates against the Washington Department of Revenue (dor.wa.gov) before filing.