About Us
Three family members, two Enrolled Agents, and five decades of experience serving businesses across the Treasure Valley.
A Family Practice
50+
Years Experience
200+
Clients Served
Castell Tax Experts is a family-run firm serving businesses across Nampa, Boise, and the wider Treasure Valley. Diane Castell founded the practice after decades working in public accounting, and today she's joined by her son Graysen. Between them, the team handles everything from monthly bookkeeping to complex tax strategy and IRS representation.
Diane is an Enrolled Agent. That's a federal credential that authorizes her to represent clients directly before the IRS. It matters when tax situations get complicated. Instead of handing you off to an outside specialist, she handles it herself.
The focus here is on helping businesses keep more of what they earn. That means identifying every deduction and credit available, staying current on tax law changes, and planning ahead instead of scrambling every April. Most business owners leave money on the table during tax season because nobody is paying close enough attention to the opportunities. We pay attention.
We work with over 200 clients, but we're not trying to grow as fast as possible. We'd rather have real relationships with the businesses we serve. Questions are encouraged. You can call anytime, not just during tax season. The answer won't cost extra, and you won't have to explain your situation from scratch every time you reach out.
Meet the Team
Diane Castell didn't choose accounting. She grew up in it. She started working alongside her CPA father at 18, earned her accounting degree from Weber State University, and never looked back. Five decades later, she's built a career spanning public accounting firms, tax preparation, and private practice.
She became an Enrolled Agent in 2008, earning the federally-licensed credential that authorizes her to represent clients directly before the IRS. When tax issues get complicated, she doesn't hand you off to someone else. She handles it. After 50 years in this business, Diane has seen tax codes rewritten, economies shift, and more tax seasons than most accountants will see in an entire career. That experience shows up in the work. There aren't many situations she hasn't dealt with before.
Graysen Castell rounds out the team. He's been with Castell Tax Experts since day one, trained in-house in accounting and bookkeeping. He manages the detailed ongoing work that keeps clients' books accurate and current throughout the year. When he's not working on client files, you might catch him hosting trivia night around town.
The Treasure Valley's Tax and Accounting Team
The Next Step:
A Short Conversation
Tell us what you're dealing with. We'll listen, answer your questions, and give you a straightforward quote.