Endsource is a tax, legal, and financial services firm based in Austin, Texas.


Endsource is a tax, legal, and financial services firm based in Austin, Texas.


Endsource is a tax, legal, and financial services firm based in Austin, Texas.




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Tax Services

Endsource provides an array of tax services for individuals and companies varying in industry and size. With depth of experience in federal, state, and international taxation issues, we assist clients in developing effective and efficient tax strategies.

We offer the following Tax Services:
Tax Compliance
  • Preparation & review of Federal, State & local tax returns
  • Preparation & review of State sales & use tax returns, and Federal excise tax returns
Income Tax & Sales & Use Tax Consulting
  • Tax Compliance
  • Tax Accounting
  • Business Planning
  • Tax Structuring
  • Accounting Methods
  • Research & Development Tax Credits
  • Foreign Withholding Tax Compliance
  • Foreign inbound transactions
Tax Controversy & Resolution Assistance
  • Federal & State income tax audit representation
  • Sales & use tax audit representation
  • Developing technical arguments and drafting advisory opinions


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Financial Services

Endsource provides a variety of financial services to individuals and companies, with a focus on accounting and investor reporting.

Our Services Include:
Technical Accounting Consulting
  • Assistance with analysis of complex revenue recognition transactions
  • Purchase accounting assistance
  • Assistance with Partnership accounting
  • Stock-based compensation consulting
Investor Reporting
  • Distribution waterfall analysis
  • Capital account maintenance
  • Income/Loss allocation
  • Financial statement reporting


We serve companies and individuals across a variety of industries and are keenly aware of both the opportunities and unforeseen consequences that can be created by the tax, legal, and financial positions of our clients. Our goal is to assist clients in capturing opportunities while avoiding unforeseen consequences.  We are also committed to establishing a relationship that best meets our clients’ needs.   Whether they seek collaboration that leverages and aligns our expertise and experience with their own, or whether they expect results with little input or guidance from them – or somewhere in-between – we are always responsive to our clients and proactive in advising them on potential or emerging issues, trends, and developments.

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Industry Experience

  • Startups
  • Biotechnology
  • Software
  • Real Estate
  • Professional Services
  • Entertainment
  • Construction
  • Financial
  • Wholesale
  • Retail




Contact Information

Nathaniel H. Lounsbury


Nathaniel H. Lounsbury, Endsource

Principal / Owner

Nathaniel Lounsbury, Endsource
Principal/ Owner

Nathaniel Lounsbury advises clients on a range of tax, accounting, real estate, business, and intellectual property issues. After working with one of the Big Four accounting firms and with a local accounting firm in Austin, he decided that smaller businesses and individuals had a real need for an advisor who could offer them a full span of services focused on meeting their specific needs; who could serve as partner and guide in navigating the many tax, legal and accounting issues that arise from the formation and operation of businesses. He established Endsource to provide an integrated array of tax, legal, and accounting services tailored to the entrepreneurial nature and needs of Austin companies and individuals.

Nathaniel has worked with both individuals and corporations. In addition to tax planning and preparation for individuals, he has advised individual investors on the tax implications of investments. He has structured investment vehicles for the purpose of real estate and commercial development and has advised on securities laws pertaining to raising capital for real estate and other commercial investments.

Corporate clients range from start-ups to small/ middle market businesses across a variety of industries including biotechnology, software, real estate, professional services, entertainment, financial, and wholesale/ retail. His practice spans the full range of business services, including contracts, operating agreements, licensing agreements for intellectual property, and employee benefits. His experience in tax planning, accounting and compliance is both deep and broad and has ranged from preparation/ review of federal, state and local tax returns to tax controversy matters and audit representation. Assisting clients in developing effective tax strategies through tax planning and through structuring transactions and agreements to maximum tax benefits and minimize risks is at the core of his service.

Before becoming attorney, Nathaniel worked with Thomson Financial (now Thomson Reuters) developing and designing financial software for the financial service industry.

Nathaniel earned his J.D. at the University of Richmond School of Law, Richmond Virginia. He has a B.S, Computer Science from the University of Maryland, College Park.
Bar Admissions: Texas, Virginia.