No Written Partnership Agreement? What the Default Rules Say in Arizona, California, and Texas

Many businesses begin informally: two people have an idea, divide responsibilities, start building, and assume they will “figure out the paperwork later.” One person may write the code. Another may bring capital, customers, operations, or sales. At the beginning, a written partnership agreement can feel unnecessary.

The problem usually appears later — when revenue arrives, expenses grow, one person wants out, a product becomes valuable, or the founders disagree about who owns what.

If there is no written agreement, the answer is not necessarily “there are no rules.” In Arizona, California, and Texas, state partnership statutes may supply default rules. Those rules can affect ownership economics, management rights, authority to bind the business, and personal liability.

This article explains the default legal framework at a high level. It is designed for founders, technical partners, small-business owners, and collaborators who may be operating without a written founders’ agreement, operating agreement, or partnership agreement.

Important: default rules are not a substitute for legal advice. Whether a partnership exists, what the parties agreed to, and who owns business assets or intellectual property depends on specific facts and state law.

1. You May Have a Partnership Even If You Never Used the Word “Partner”

A common misconception is that a partnership exists only if the parties sign a document called a “partnership agreement.” That is not how general partnership law usually works.

In broad terms, Arizona, California, and Texas all recognize that a partnership may arise from the parties’ conduct. The statutory formulations differ slightly, but the core idea is similar: when two or more persons associate to carry on a business as co-owners for profit, a partnership may exist even if they did not file formation documents or use formal partnership language.

• Arizona: A partnership can be formed under Arizona’s partnership statute when the statutory requirements are met, and Arizona recognizes rules for determining whether a partnership has been formed. See A.R.S. § 29-1012.
• California: California Corporations Code § 16202 provides rules for determining whether an association is a partnership, including the concept of an association of two or more persons to carry on as co-owners a business for profit. See Cal. Corp. Code § 16202.
• Texas: Texas Business Organizations Code § 152.051 addresses partnership formation, and § 152.052 lists factors indicating that persons have created a partnership, including profit sharing, expressions of intent, participation in control, and contributions. See Tex. Bus. Orgs. Code ch. 152.

That means an informal “handshake” business arrangement can create legal consequences. Sharing profits is often important evidence, but it is not the only fact courts or lawyers may examine. Control, contributions, representations to others, bank accounts, tax filings, contracts, emails, text messages, and course of performance may all matter.

If you are searching for “no written partnership agreement,” “handshake partnership,” or “startup founders agreement,” the threshold question is often not whether a formal agreement exists. It is whether the facts show that the parties created legal rights and obligations anyway.

2. Default Rule: Profits May Be Shared Equally Unless the Parties Agree Otherwise

One of the most surprising default rules is the treatment of profits. Many founders assume that profit shares automatically track contributions: more cash, more work, more code, more customers, or more risk should mean a larger share.

The default partnership rules do not necessarily work that way. In Arizona and California, the partnership statutes generally provide that each partner is entitled to an equal share of partnership profits unless the partners have agreed to a different arrangement. Texas partnership law also contains default economic rules that may apply unless otherwise agreed.

• Arizona: A.R.S. § 29-1031 addresses partners’ rights and duties and includes default rules on profit and loss sharing.
• California: Cal. Corp. Code § 16401 provides that each partner is entitled to an equal share of partnership profits and is chargeable with a share of losses in proportion to the partner’s share of profits.
• Texas: Texas Chapter 152 supplies default rules for partnerships, including rules that may govern partner rights, duties, and liabilities absent a contrary agreement.

This can surprise both sides of an informal founder relationship:

• A capital contributor may assume that investing most of the money means receiving most of the profits.
• A technical founder may assume that building the product creates equity or a larger economic share.
• A sales-focused founder may assume that bringing customers controls the economics.
• A part-time collaborator may assume informal involvement does not carry full partner consequences.

The safer approach is to document the economics in writing. A written partnership agreement, LLC operating agreement, stockholder agreement, or founders’ agreement can specify ownership percentages, profit distributions, losses, capital accounts, vesting, compensation, reimbursement, and buyout rights.

3. Default Rule: Equal Management Rights Can Create Deadlock

Default partnership rules often give partners equal rights in management and conduct of the partnership business, subject to statutory rules and any agreement among the partners.

For two-person businesses, equal management rights can become a structural problem. If both people have an equal say and no agreed tiebreaker, a disagreement can freeze the business. This is especially common in 50/50 founder relationships, where neither person can force a decision and neither person has a clear exit process. We’ve written separately about how to protect yourself in a 50/50 partnership.

• Arizona: A.R.S. § 29-1031 includes default rules addressing management rights, ordinary-course decisions, matters outside the ordinary course, and amendments to the partnership agreement.
• California: Cal. Corp. Code § 16401 includes default rules concerning equal rights in management, ordinary-course decisions, and matters outside the ordinary course.
• Texas: Texas partnership law contains default provisions governing the relations among partners and the business. See Tex. Bus. Orgs. Code ch. 152.

A written agreement can reduce deadlock risk by addressing: who controls ordinary-course business decisions; what decisions require unanimous consent; whether one founder has final authority in a defined area; what happens if the founders cannot agree; buy-sell rights, shotgun provisions, mediation, or other exit procedures; removal, resignation, disability, death, and withdrawal; and what happens if one person stops contributing.

4. Default Rule: A Partner May Be Able to Bind the Business

Another major issue is authority. In a general partnership, a partner may have authority to act as an agent of the partnership for business conducted in the ordinary course.

That does not mean every act by every partner always binds everyone in every circumstance. Statutory exceptions, notice, authority limitations, the ordinary course of the business, and third-party knowledge may matter. But as a general risk point, informal partners should not assume they are insulated from one another’s business commitments.

• Arizona: A.R.S. § 29-1021 addresses a partner’s agency authority and when a partner’s act may bind the partnership.
• California: Cal. Corp. Code § 16301 addresses a partner’s authority as an agent of the partnership.
• Texas: Tex. Bus. Orgs. Code § 152.301 addresses partner liability, and other provisions in Chapter 152 address partner authority and partnership obligations.

This matters when a partner signs a vendor contract, takes on debt, commits to deliverables, hires contractors, leases space, opens accounts, or makes representations to customers.

A written agreement can help by defining signing authority, spending limits, approval rights, bank-account controls, customer-contract procedures, and restrictions on debt. In some cases, forming an LLC or corporation may also help manage personal-liability risk, although entity formation alone does not replace the need for clear internal agreements.

5. Default Rule: General Partners May Face Personal Liability

The most serious consequence of an informal general partnership is potential personal liability.

A general partnership is different from an LLC or corporation. Without a liability-limiting entity structure and proper separateness, partners may be personally responsible for partnership obligations under applicable law. That exposure may include contracts, debts, and certain wrongful acts connected to partnership business.

• Arizona: A.R.S. § 29-1026 addresses partner liability for partnership obligations, and A.R.S. § 29-1025 addresses partnership liability for a partner’s actionable conduct.
• California: Cal. Corp. Code § 16306 addresses partner liability, and related provisions address partnership liability.
• Texas: Tex. Bus. Orgs. Code Chapter 152 includes provisions addressing partner liability and partnership liability for partner conduct, including §§ 152.301 and 152.304.

This is why “we never signed anything” is not always comforting. If the relationship legally functions as a partnership, the absence of paperwork may increase uncertainty rather than eliminate risk.

For founders, the risk-control question is usually not just “Do we have a partnership agreement?” It is also:

• Have we formed the correct legal entity?
• Are contracts signed by the correct party?
• Are business and personal funds separated?
• Is there written authority for major commitments?
• Are tax, employment, IP, and ownership records consistent with the intended structure?

6. The Technical Co-Founder Problem: “I Built the Product, but We Never Signed an Equity Agreement”

A common version of the no-written-agreement problem involves a technical partner or developer who builds software, a platform, a website, an app, or other intellectual property based on an informal promise of future equity. Searches like “protect yourself as technical partner no equity agreement” often come from this situation.

The legal analysis can be fact-intensive. A few issues often matter:

Ownership of the company is separate from contribution of work

If an LLC or corporation was formed, ownership usually depends on the company’s governing documents and issuance records. A person may have contributed valuable work without automatically receiving membership interests, shares, or equity. Conversely, informal conduct and communications may create contract, partnership, compensation, or equitable arguments depending on the facts.

Intellectual property ownership is separate from business ownership

Writing code does not always answer who owns the company, and forming a company does not always answer who owns the code. IP ownership may depend on employment status, contractor agreements, assignment language, work-made-for-hire rules, contribution history, and the specific type of intellectual property involved.

For software startups, this is a major diligence issue. Investors, buyers, and future partners often want to confirm that the company owns or has valid rights to the product it is selling.

Informal promises can matter, but proof matters too

Texts, emails, pitch decks, cap tables, tax records, payment records, GitHub history, customer communications, and witness testimony may all be relevant. The practical problem is that informal promises are often incomplete. “You’ll get a piece” does not necessarily answer:

• How much equity? In what entity? When does it vest?
• What happens if someone leaves?
• Is the person a founder, contractor, employee, partner, or vendor?
• Who owns the code or other IP?
• What happens if the business never raises money or never forms an entity?

The earlier these issues are documented, the easier they usually are to manage.

7. What a Written Agreement Can Change

Many partnership default rules can be modified by agreement. The right document depends on the structure. A general partnership may use a partnership agreement. An LLC typically uses an operating agreement. A corporation may use bylaws, stock purchase agreements, restricted stock agreements, IP assignment agreements, and stockholder agreements. Early-stage founders may also use a founders’ agreement before or alongside entity formation.

A well-drafted agreement commonly addresses:

• Ownership percentages: who owns what, in what entity, and when ownership is issued.
• Capital contributions: who contributes cash, equipment, services, IP, or other assets.
• Profit and loss sharing: whether distributions track ownership, capital, performance, or another formula.
• Founder vesting: whether ownership is earned over time or subject to repurchase if a founder leaves.
• Management authority: who makes ordinary-course decisions and which decisions require approval.
• Deadlock procedures: what happens when equal owners cannot agree.
• Spending and debt limits: who can sign contracts, borrow money, hire people, or bind the business.
• IP assignment: whether the company owns code, branding, content, inventions, domains, customer lists, and work product.
• Confidentiality and non-use obligations: how sensitive business information is protected.
• Exit rights: buyouts, transfers, rights of first refusal, disability, death, withdrawal, and termination.
• Dispute resolution: forum, venue, governing law, mediation, arbitration if chosen, and attorneys’ fees if appropriate.

The goal is not paperwork for its own sake. The goal is to replace uncertain default rules with business terms the founders actually chose.

8. Self-Check: Questions to Ask Before a Dispute Starts

If you are working with a business partner without a written agreement, ask these questions now:

• Are we sharing profits or presenting ourselves as co-owners of a business?
• If revenue came in tomorrow, do we know exactly how it would be split?
• If we disagreed tomorrow, who would have authority to decide?
• Can either person sign contracts, incur debt, hire contractors, or commit the business?
• Have we formed an LLC or corporation, or are we operating informally?
• If an entity exists, have ownership interests or shares actually been issued?
• Does the company own the code, brand, content, domains, customer lists, and other IP?
• What happens if one person leaves, stops working, wants to sell, or claims a larger share?
• Are our tax filings, bank accounts, invoices, contracts, and public statements consistent with what we think the arrangement is?
• Would a neutral third party understand our deal from the documents we have today?

If the answer to any of these is “I’m not sure,” that uncertainty is itself important. Default rules may answer some questions for you — but they may not answer them the way you would have chosen.

9. Practical Takeaway

A no-written-partnership-agreement situation is not automatically hopeless, and it is not automatically harmless. The key point is that the law may supply default answers when founders do not create their own. Those default answers can affect: whether a partnership exists; who shares profits and losses; who controls business decisions; who can bind the business; who may be personally liable; and who owns the company’s assets and intellectual property.

For founders, technical partners, and small-business collaborators, the best time to clarify the arrangement is before the business becomes valuable or the relationship becomes strained. If you are building, funding, or operating a business with someone else and do not have the deal in writing, consider speaking with a business attorney in your state before relying on assumptions.

Frequently Asked Questions

This FAQ is for general informational purposes only and does not create an attorney-client relationship. Whether a partnership exists and what its terms are is highly fact-specific, and the result can depend on the conduct of the parties, entity documents, and applicable state law.