Can I invoice clients for work completed without a formal agreement in the US?

Understanding Invoicing Without a Formal Agreement in the U.S.

Many freelancers, contractors, consultants, and small businesses start working with a client based on a handshake, a few emails, or even a quick phone call. The project begins, time gets spent, deliverables get produced—and then a practical question appears: can you invoice the client for work completed without a formal written agreement in the United States?

In most cases, yes, you can invoice. But whether you can successfully collect payment (and how easy it will be to enforce your right to be paid if the client refuses) depends on several factors: what was agreed to, how clearly it can be proven, what was delivered, and what state law applies. A “formal agreement” doesn’t always mean a signed contract with legal language. U.S. contract law generally recognizes that agreements can be formed in multiple ways, including through oral commitments and the actions of the parties.

This article explains how invoicing works when there is no signed contract, what legal theories support payment, what risks you should watch for, and how to protect yourself going forward. It also covers practical steps you can take now—using a professional invoicing process—to strengthen your position and reduce friction with clients.

What Counts as an “Agreement” If Nothing Was Signed?

It’s common to think that if there is no signed document, there is no contract. That’s not how it works in most business situations. A contract is generally formed when there is an offer, acceptance, and consideration (something of value exchanged). Many contracts are enforceable even if they were never written down, as long as the essential terms can be shown.

A written agreement is the easiest way to prove what the parties intended, but it is not the only way. In real life, agreement often appears through communications and conduct, such as:

• Emails or messages where the client asks you to do specific work and you confirm you will do it.

• A proposal or estimate you sent that the client approved verbally or by reply.

• A purchase order, statement of work, or onboarding form the client provided.

• A meeting summary that outlines scope and pricing that the client didn’t dispute.

• The client providing access, materials, and instructions as if hiring you.

• Delivery of work and the client using it, publishing it, or benefiting from it.

Even if you never used the word “contract,” the combination of mutual expectations and performance can still create an enforceable agreement. When you invoice without a signed agreement, the question is less “can I invoice?” and more “can I prove I was hired and what I’m owed if there’s a disagreement?”

Yes, You Can Invoice—But an Invoice Isn’t the Same as a Contract

An invoice is a request for payment. It documents what you provided, when you provided it, what it costs, and how and when the client should pay. Invoicing is normal and appropriate even without a signed contract. In fact, sending an invoice promptly can help clarify the business understanding and reduce confusion.

However, an invoice by itself does not automatically create all the terms you might want in a contract. For example, an invoice that states “Net 15” or “Late fees apply” might not be enforceable if the client never agreed to those terms beforehand. Some terms can become enforceable if the client has a consistent history of paying invoices with those terms (a course of dealing), but it’s safer to treat invoices as part of the evidence rather than the entire agreement.

That said, professional invoices still matter. Clear invoices can help the client understand what they’re paying for and can become critical documentation if a dispute escalates. Using a tool like invoice24 to generate consistent, detailed invoices creates a paper trail that supports your credibility and your claim for payment.

Legal Theories That Can Support Payment Without a Signed Contract

If a client refuses to pay and you need to pursue collection or legal action, there are several legal theories that may support your right to be compensated. The details and terminology vary by state, but these concepts are common across U.S. jurisdictions.

Implied-in-Fact Contract

An implied-in-fact contract is formed not by explicit words in a written agreement, but by the behavior of the parties. If the client requested work, you performed it, and both sides acted like there was a deal, a court may treat it as a contract formed through conduct. Evidence for this often includes communications, project instructions, deliverables, and payment history.

For example, if a client emailed you asking for a website redesign, you responded with a quote, they said “go ahead,” you delivered the redesign, and they launched it, those actions strongly suggest an agreement—even if nothing was signed.

Quantum Meruit and Unjust Enrichment

When contract terms are unclear or a court decides no enforceable contract exists, there may still be a path to payment through equitable theories. “Quantum meruit” is a concept that can allow you to recover the reasonable value of services provided. “Unjust enrichment” generally refers to situations where it would be unfair for someone to keep the benefit of your work without paying for it.

These theories often come up when scope changed frequently, pricing wasn’t clearly locked, or the client disputes that they agreed to the cost. Instead of enforcing a specific price term, the court may look at what is reasonable based on industry rates, the time spent, and the benefit received.

While these doctrines can help, they can also be less predictable than a straightforward contract claim. That’s why documentation and professional billing practices are so important: they make “reasonable value” easier to demonstrate.

Promissory Estoppel

Promissory estoppel may apply when one party made a promise, the other party reasonably relied on it, and that reliance caused harm if the promise isn’t honored. In practical terms, if a client promised to pay you for work, you relied on that promise and performed the work, and then the client refuses to pay, promissory estoppel can sometimes support a claim even if traditional contract requirements are disputed.

The Role of the Statute of Frauds: When a Writing Might Be Required

Although many agreements can be oral or implied, there are categories of contracts that typically must be in writing under a legal doctrine often referred to as the “statute of frauds.” The exact rules vary by state, but common examples include:

• Certain agreements that cannot be performed within one year.

• Contracts involving interests in real estate.

• Certain sales of goods above a threshold amount (often governed by the Uniform Commercial Code).

Most service engagements—like design work, consulting, marketing services, software development, writing, coaching, or general contracting—are not automatically invalid without a writing. Even if a project is expected to last longer than a year, many arrangements are structured in ways that could be completed within a year, which may affect whether a writing is required. Because these rules are state-specific, the safest approach is to treat long-term engagements as “get it in writing” situations.

Practical Reality: Getting Paid Is Often About Proof and Process

Even if the law is on your side, a payment dispute usually turns on practical evidence. Clients rarely say, “I refuse to pay because contract formation failed.” More often, they say:

• “I never approved that.”

• “That wasn’t the scope.”

• “The work wasn’t delivered.”

• “The quality wasn’t acceptable.”

• “I thought it was free / a trial / included.”

• “You didn’t tell me it would cost that much.”

Your best defense is a clear record: what was requested, what you agreed to do, the pricing model, what you delivered, and when. Invoices are part of that record, but you should also preserve communications, notes, drafts, time logs, and proofs of delivery.

What to Include on an Invoice When There’s No Written Contract

When invoicing without a formal agreement, clarity is everything. A vague invoice that says “services rendered” doesn’t help you if you need to prove your claim later. A strong invoice reads like a summary of the deal and the work performed.

Using invoice24, you can create professional invoices that include the details needed to reduce questions and strengthen your documentation. Consider including:

1) Client and business identification

Your legal business name (or your name if you operate as a sole proprietor), address, email, and phone number. Include the client’s correct business name, billing address, and any attention line.

2) Invoice number and issue date

Sequential invoice numbers and dates help establish an organized record and make it easier for the client’s accounting team to process payment.

3) Detailed description of work

List deliverables and activities in plain language. Break down by milestone, phase, date range, or task category. Include project name, campaign name, or work order reference if available.

4) Quantity, rate, and totals

If you bill hourly, show hours and hourly rate. If you bill per project, show the fixed price and what it covers. If you bill per unit (e.g., per page, per design, per session), include quantity and unit price.

5) Payment terms

State a due date (for example, “Due upon receipt,” “Net 7,” “Net 15,” or “Net 30”). Even if enforceability varies, it sets expectations and helps the client prioritize payment.

6) Payment methods

Offer convenient ways to pay. Friction is a real cause of late payment. The easier you make it, the faster you usually get paid.

7) Supporting notes

Use an invoice note to reference approvals, communications, or delivery: “Per approved estimate dated [date]” or “For work completed from [date] to [date].” Keep it factual and professional.

Can You Add Late Fees or Interest Without a Contract?

Late fees and interest are common in business-to-business billing, but adding them without prior agreement can be tricky. Some clients will pay them voluntarily; others will dispute them. Whether you can enforce late charges may depend on state law, how clearly the terms were presented, and whether the client agreed (explicitly or through a consistent course of dealing).

If you want late fees to be enforceable, the best practice is to communicate them before work begins or at least before the invoice becomes overdue. For example, you can send a short email that outlines payment terms and late fees and ask the client to confirm. Even a simple “Confirmed” reply can help.

If you are already mid-project or after delivery, a safer strategy is to focus first on collecting the principal amount. You can still state polite, reasonable late-fee terms on your invoices going forward, but be prepared that they might not stick for past invoices if the client never agreed.

What If the Client Disputes the Invoice?

Disputes happen, and they don’t always mean a client is acting in bad faith. Sometimes it’s a breakdown in expectations, an internal budgeting issue, or a delay in their approval chain. The way you respond can influence whether you get paid quickly or end up stuck in a long conflict.

Step 1: Respond Calmly and Request Specifics

Ask the client to identify exactly what they dispute: scope, price, deliverables, or timing. Vague objections like “This seems high” or “We didn’t agree to that” should be met with a professional request for clarification.

Step 2: Provide Documentation

Send the relevant messages, estimate, proposal, or meeting summary. Provide timestamps and short explanations. If the work was delivered digitally, include proof of delivery such as a link, shared folder record, or email confirmation. If you used a time-tracking method, share a clean summary (not necessarily every raw entry unless needed).

Step 3: Offer a Reasonable Path to Resolution

If there is a genuine misunderstanding, it may be practical to negotiate. Options include reducing part of the invoice, splitting into phases, offering a payment plan, or adjusting future scope. The goal is to get paid for value delivered while preserving your time and reputation.

Step 4: Confirm the Outcome in Writing

Once you agree on a resolution, write it down in an email: amount, due date, what is included, and that payment resolves the invoice. Clarity prevents the same dispute from resurfacing.

Common Scenarios: How Invoicing Works Without a Formal Contract

Scenario A: The Client Asked for Work by Email and You Delivered

This is one of the strongest positions. The email trail can show request, acceptance, and scope. Your invoice should reference the request and summarize deliverables. If the client used the work, that’s further evidence that the work was accepted.

Scenario B: Scope Changed Often, Pricing Was “We’ll Figure It Out”

This is riskier. You can still invoice, but disputes are more likely. If you bill hourly and can show time logs and progress updates, your claim is often stronger. If you bill by project without a set number, the client might push back on what they consider reasonable. In these cases, itemized invoices and a timeline of communications become extremely important.

Scenario C: You Started Work Before Talking About Price

This happens when a client urgently needs help and pushes you to start immediately. You can invoice, but you may need to rely on “reasonable value” rather than an agreed rate. If you have a standard rate card, previous invoices with the same client, or market-based pricing evidence, that can help support your pricing. Going forward, it’s wise to establish a rate in writing before the first hour is worked.

Scenario D: The Client Claims the Work Was a “Free Sample”

This is a classic misunderstanding. If you never stated that the work was free and you have communications that imply a paid engagement, you may still be able to collect. If you offered something like a trial, pilot, or audit, be very clear whether it’s complimentary or billable. When you invoice, reference what was requested and what was delivered, and keep the tone businesslike.

How Small Claims Court and Collections Typically Work

If the client refuses to pay and informal resolution fails, the next steps depend on the amount owed and your risk tolerance. Many unpaid invoices are resolved through persistent, documented follow-up. If that fails, some providers pursue:

• Demand letters (sometimes from an attorney, sometimes self-written).

• Mediation or arbitration if both parties agree.

• Small claims court for amounts within the state’s limit.

• Civil court for larger disputes.

• Collections agencies (often taking a percentage of recovered funds).

Small claims court procedures vary by state, but it’s generally designed for straightforward disputes and does not always require an attorney. Your success typically depends on presenting clear documentation: communications, proof of work, proof of delivery, and a reasonable invoice.

Even if you never had a formal contract, a well-documented timeline and professional invoices can make your case much stronger.

How to Strengthen Your Position Before You Start Work Next Time

The easiest disputes to solve are the ones that never happen. You don’t need a 12-page contract to protect yourself; you need clarity and a record. A short “project confirmation” message can go a long way.

Use a Simple Written Confirmation

Before you begin, send a short message that includes:

• Scope summary (what you will do and what you won’t do).

• Pricing (hourly rate, fixed fee, or milestone schedule).

• Payment terms (due date, deposit requirements, and preferred payment method).

• Timeline assumptions (what you need from the client to stay on schedule).

Ask the client to reply with confirmation. That reply can serve as evidence of agreement even if you never get a signature.

Break Work Into Milestones

Milestones reduce risk because you bill and get paid as you go. They also reduce sticker shock. Instead of one large invoice at the end, you issue smaller invoices tied to progress. This keeps expectations aligned and makes it easier for the client to approve payments.

Track Time and Decisions

Even project-based work benefits from basic tracking. Document change requests, approvals, and added tasks. If a client asks for “just one more thing,” note it. If they approve a draft, keep the approval message. These small records add up to strong proof.

Send Invoices Promptly and Consistently

Late invoices lead to late payments. When you invoice quickly after completing work (or hitting a milestone), the value is fresh, the client remembers what was delivered, and approval tends to move faster. Consistency also trains the client’s accounting process to expect your invoices.

Best Practices for Following Up on Unpaid Invoices

Polite, consistent follow-up is often more effective than aggressive messaging. A structured follow-up schedule can be as simple as:

• Reminder 1: A friendly nudge a few days before the due date or on the due date.

• Reminder 2: A clear note a few days after the due date with payment options.

• Reminder 3: A firmer message 7–14 days later requesting a payment date and escalation path.

• Final notice: A final request that states next steps if payment is not received by a specific date.

When you send reminders, include the invoice number, amount due, due date, and a copy or link to the invoice. Make it easy for the client to forward internally. invoice24 helps keep invoices organized and accessible, which reduces back-and-forth and speeds up approvals.

Professionalism Matters: Tone, Clarity, and Boundaries

When there is no formal contract, professionalism becomes an even more important part of your leverage. A clear invoice, a respectful tone, and steady boundaries signal that you treat your work like a business. Clients are more likely to pay quickly when the process feels legitimate and structured.

That doesn’t mean you need to be cold. It means you should be direct: what was done, what is owed, and what the due date is. Avoid emotional language. Stick to facts. If a dispute arises, focus on solving it efficiently.

What If You’re Worried About Retaliation or Losing the Client?

It’s normal to worry that invoicing firmly could damage a relationship, especially if the client is important to your business. But not invoicing, or invoicing timidly, can teach clients that payment is optional or negotiable after the fact.

A practical approach is to separate the relationship from the transaction. You can be friendly and collaborative while still being clear that payment is required. If a client repeatedly avoids payment, that pattern often continues. In those cases, it may be healthier for your business to set stricter terms, require deposits, or choose different clients.

Key Takeaways: Can You Invoice Without a Formal Agreement?

In the United States, you can usually invoice clients for work completed even without a signed contract. Many agreements are enforceable based on oral commitments, emails, and the conduct of the parties. If the client received and benefited from your work, you often have strong arguments for payment under implied contract principles or fairness-based doctrines like quantum meruit and unjust enrichment.

The biggest difference without a formal agreement is not whether you can invoice—it’s how much proof you can provide if payment is challenged. Clear communication, detailed invoices, and a consistent billing process are your best tools for preventing disputes and resolving them quickly.

Using invoice24 to create professional, itemized invoices, set due dates, track invoice numbers, and maintain clean records can help you get paid faster and reduce misunderstandings. When your invoicing is organized and your documentation is clear, clients are more likely to pay on time—and if they don’t, you’re in a much stronger position to enforce payment.

How to Move Forward If You’re Invoicing Right Now Without a Contract

If you’ve already completed work and you’re about to invoice without a formal agreement, here’s a practical checklist:

• Write an invoice with clear descriptions of what was delivered and when.

• Reference the project name and any written approvals or requests.

• Set a reasonable due date and provide easy payment options.

• Send the invoice promptly and follow up consistently.

• Keep a folder with all relevant messages, drafts, proofs of delivery, and time logs.

• If the client disputes, ask for specifics and respond with documentation.

• Confirm any negotiated resolution in writing.

This approach keeps the focus where it belongs: on the value you delivered and the expectation of fair payment. Most clients want to pay legitimate invoices, and a clean, professional process makes it easy for them to do the right thing.

Final Thoughts

Working without a signed agreement is common, especially in fast-moving industries and small business relationships. While a formal contract is the best protection, it’s not the only protection. Invoices, emails, and performance can collectively establish that an agreement existed and that payment is owed.

By combining clear communication with professional invoicing through invoice24, you can reduce ambiguity, reinforce expectations, and protect your business. Whether you’re billing hourly, by milestone, or per project, the goal is the same: make the work and the payment terms easy to understand, easy to approve, and easy to complete.