Tax Services
Seattle, WA
Located in North Seattle, Withum is a leading Seattle CPA firm with a robust ERISA practice, enhanced forensic capabilities and the ability to offer outsourced accounting and cybersecurity services locally and nationwide.
Ranked in the top 25 firms in the nation, Withum’s team of passionate professionals offer advisory, tax, audit and assurance services to the Seattle business community…plus a whole suite of advisory solutions that will level up your success. That’s the Power in the Plus!
(206) 522 6370
Seattle Service Specializations
Assurance and Accounting
Forensic and Valuation Services
Cybersecurity
Outsourced Accounting Systems and Services (OASyS)
Washington State and Local Tax Updates
Do you or your organization operate in multiple states? Do you own property in a variety of states? Washington State and Local Tax (SALT) laws are always changing and understanding the nuances of the states that you own or operate in is challenging. In these Washington resources, you’ll find just a dash of the most up-to-date details on rules and regulations as state and local tax changes happen by state!
Industries We Focus on in Washington
Beyond the Region
- Inside Public Accounting Top 100 Firms – 22nd Largest Nationally
- Accounting Today Top 100 Firms – 22nd Largest Nationally
- Great Place to Work® – Fortune Best Workplaces for Parents and Women
- Vault Top 25 Accounting Firm
Partner In Charge
Joseph M. Thiermann, CPAJoe is a partner with over 25 years of specialized audit experience with audits of defined contribution plans, defined benefit plans, health and welfare plans, labor organizations and not-for-profits. He conducts system-wide reviews, designs and implements accounting systems and works on special projects involving system design, expense reporting and compliance, often in conjunction with other professionals to resolve regulatory and general management issues for clients.
Joe is an avid public speaker, having presented at the Annual Conference of the International Foundation of Employee Benefit Plans (IFEBP), the IFEBP Accountants’ Institute and the Oregon Labor Law Conference, and even taught business courses to contractors.
Seattle Leadership
Withum in the News
Stephanie Mansour Named a Financial Services Woman to Watch by Providence Business News
Stephanie is a growth driver at Withum, leading audit engagements across various industries, including not-for-profit, industrial and consumer products, healthcare and employee benefit plans. She brings a strategic approach to identifying risk and performing internal control testing to support accurate, reliable financial reporting for her clients. Stephanie oversees complex engagements while working with her team…
Withum Announces 2026 Firmwide Leadership Transitions
This next generation of leaders step forward at a pivotal time for the Firm, bringing the technical expertise and strategic perspective needed to navigate continued growth, rapidly advancing technology and an ever-evolving industry landscape. Grounded in the Withum Way mentality, they will shape what’s ahead while preserving the culture that remains central to how the…
Withum Names Eighteen New Partners
Introducing Our 18 New Partners
Withum’s Columbia Office Welcomes Greater Baltimore
Withum team members, clients and community leaders, including representatives from Howard County and the Central Maryland Chamber, came together to mark the official “door opening” on the new location. The ribbon-cutting ceremony highlighted the evening, which featured citations presented by community leaders welcoming Withum to the Columbia region and recognizing its strong ties to the…
Nadia Matthie Appointed as Chair of the AICPA’s Employee Benefit Plans Expert Panel
The AICPA’s Employee Benefit Plans Expert Panel was formed to protect the public interest and agree on key plan issues by leveraging the knowledge of leaders in the employee benefit plan industry. Nadia’s deep expertise makes her a valuable asset to help further the panel’s mission as Chair of the group. Nadia has more than…
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