What’s the best way to invoice clients for usage-based consulting services in the US?

Can I invoice clients for work completed before formal onboarding in the US?

If you’ve ever started work “just to keep things moving” before a client signed your contract, completed paperwork, or finished vendor onboarding, you’re not alone. In the real world—especially with fast-moving startups, agencies, and busy procurement teams—work often begins before the administrative steps catch up. The question is whether you can invoice for that work in the United States, and if so, how to do it without creating disputes, compliance problems, or payment delays.

The short practical answer is: yes, you usually can invoice for work performed before formal onboarding, as long as the work was authorized (explicitly or implicitly) and you can document what you did, when you did it, and why you reasonably believed you were approved to proceed. The longer and more important answer is that your ability to get paid depends on contract principles, proof, client procurement rules, your classification as a vendor, and how you present the invoice. This article walks through the legal and operational realities, common risk scenarios, and best practices you can use to bill confidently and get paid faster.

What “formal onboarding” typically means (and why it matters)

When people say “formal onboarding,” they might mean different things depending on the client. For a small business, onboarding could be as simple as signing an agreement and exchanging W-9 details. For a large company, onboarding can include vendor registration, supplier compliance checks, purchase order requirements, insurance verification, background checks, data security questionnaires, and approval to access systems.

Onboarding matters because many organizations treat it as the gateway to payment. A client’s accounts payable team may be instructed not to pay invoices unless the vendor is in the system, the invoice references a purchase order, or the contract is fully executed. None of those internal rules automatically erase your right to be paid for authorized work, but they can create a very real payment obstacle.

So you’re juggling two different questions at once:

First, do you have a legal basis to charge for work already performed? Second, can the client’s internal processes actually pay you without pushing the invoice into limbo? A smart invoicing approach considers both.

The core legal concept: you can be owed money even without a signed contract

In the US, you do not always need a signed, formal contract to have an enforceable agreement. Contracts can be formed through written communications (like email), oral agreements, or even conduct—where both sides behave as though a deal exists. If the client requested work and you performed it with the expectation of payment, that can create legal obligations.

Two ideas show up repeatedly in disputes about “pre-onboarding” work:

Implied-in-fact contract: This is an agreement inferred from the actions and communications of the parties. For example, a client asks you to begin design work, you send deliverables, they provide feedback, and the project proceeds as though you’ve been hired. Even if the contract document wasn’t signed, the conduct can suggest mutual assent.

Equitable claims (often described as unjust enrichment or quantum meruit): These are concepts used when there is no enforceable contract, but one party received a benefit and it would be unfair for them not to pay for it. If your work created value and the client accepted or used it, you may have a claim for reasonable compensation.

This does not mean every pre-onboarding invoice is automatically collectible. It means there is often a legal theory supporting payment, especially where authorization and acceptance are clear. The stronger your documentation, the less this feels like a “legal debate” and the more it feels like routine accounts payable processing.

Authorization is the dividing line: did the client approve you to start?

The biggest practical and legal question is whether the work was authorized. Authorization can be explicit (“Please begin immediately; we’ll finalize onboarding next week.”) or implied (“We need this by Friday; proceed and send drafts.”). It can also be conditional (“Start once procurement approves.”), which is where problems start.

When your work begins before onboarding, the invoice is most defensible if you can show:

1) The client requested or approved the work, or at least knew you were doing it and did not stop you.

2) You communicated your rates or pricing approach in advance, or the price is otherwise reasonable and consistent with industry practice.

3) The client received deliverables, provided feedback, used the work, or otherwise accepted the benefit.

Without those elements, your invoice may trigger pushback such as: “We never approved this,” “We thought it was a free trial,” or “Our onboarding policy prohibits it.” The goal is to prevent those narratives from taking root.

Common real-world scenarios and how invoiceability changes

Pre-onboarding work happens in different ways, and each has different billing risk. Here are common scenarios and what they typically imply.

Scenario 1: The client asked you to start, and you agreed on price in writing

This is the strongest position. If you have an email chain, proposal acceptance, or message confirming scope and price, invoicing is usually straightforward. Your main challenge may be logistical—getting set up as a vendor so accounts payable can pay—rather than whether the charge is legitimate.

In this situation, your invoice should reference the written authorization, include clear dates of service, and align with the stated pricing. If there is a purchase order requirement, you may need the client to create a retroactive PO or issue an exception.

Scenario 2: The client asked you to start, but price wasn’t finalized

You can still invoice, but you should take extra care to avoid sticker shock and disputes. If you have a rate card, a proposal, or prior pricing history with the client, use it. If you don’t, consider invoicing based on a reasonable rate for the market and your experience, with detailed line items and time logs.

When price wasn’t finalized, clarity is your friend. A vague invoice (“Consulting services – $5,000”) invites negotiation. A specific invoice (“Discovery workshop: 3 hours, stakeholder interviews: 6 hours, requirements summary: 4 hours”) makes the value tangible and reduces the client’s leverage to argue that the price is arbitrary.

Scenario 3: You started work “to help,” without a clear request

This is the risky zone. If you began work proactively and then presented a bill, the client may argue they didn’t authorize it. Even if they benefited, the path to payment is less predictable. You may still have a basis to request compensation—especially if the client used your work—but you should expect negotiation or partial payment.

If you are already here, it helps to frame the invoice as a request tied to tangible outputs and a reasonable value, rather than insisting it is non-negotiable. Going forward, you’ll want a “permission checkpoint” before doing billable work.

Scenario 4: Onboarding rules require a PO or signed contract before work

This is common in enterprise environments. The client may acknowledge the value of your work and still say: “We can’t pay without a PO.” In many cases, the fix is administrative, not adversarial. Ask your sponsor or project lead to engage procurement to issue a PO that covers the earlier work dates, or to approve a non-PO invoice exception.

Sometimes the company’s policy is strict, but exceptions exist with director-level approval. Your job is to make the exception request easy: provide a clean summary of services, dates, evidence of authorization, and the business justification for starting early.

Scenario 5: Government entities and certain regulated clients

If your client is a government agency or a heavily regulated entity, pre-onboarding work can be particularly complicated. Some public-sector procurement rules prohibit payment without specific authorizations. Even if an employee requested work, that person may not have authority to bind the agency.

This is where “can I invoice?” becomes “will the entity be legally allowed to pay?” In these cases, it’s especially important to understand who has authority, what approvals are required, and whether the work should be treated as a non-billable exploratory phase unless a formal contract is executed. If you do proceed, document the request, the official’s role, and any procurement guidance in writing.

What to include on a pre-onboarding invoice to maximize approval

When work occurs before onboarding, your invoice must do more than request payment. It must help the client’s internal teams validate and approve it. Make it easy for accounts payable and procurement to say “yes.”

Here are the elements that matter most:

Clear service period: List the exact dates the work was performed (e.g., “Services rendered: January 8–January 22, 2026”). Pre-onboarding invoices often fail because they feel disconnected from time.

Detailed line items: Break the work into understandable components. Avoid vague single-line invoices. If you’re billing hourly, include hours and rates. If you’re billing fixed-fee milestones, identify the milestone and deliverable.

Scope description: Add a concise narrative: what you did, why you did it, and what the client received. Keep it factual and aligned to the business outcome.

Reference to authorization: Include the name of the client contact who authorized the start, and the date of that authorization. Some vendors include a note such as: “Work initiated at request of [Name, Title] on [date].” You are not trying to be threatening; you’re making approvals traceable.

Supporting documents available: You don’t need to attach everything to the invoice, but you should be prepared to provide the proposal, email approval, time logs, and deliverables upon request.

Payment terms that fit the client: If the client pays on Net 30, using Net 7 might provoke delay. Reasonable terms reduce friction. If you need faster payment, consider offering early-payment incentives rather than aggressive terms.

Vendor information and tax details: Include your business name, address, and taxpayer information where appropriate. Many clients will request a W-9; be ready to provide it promptly.

Purchase order field: If the client might later issue a PO, leave room for a PO number, or mark it as “PO pending” so the invoice can be updated without reissuing a brand-new document.

How to word the invoice note without sounding confrontational

One challenge with pre-onboarding billing is tone. You want to be firm, but you don’t want to escalate. A short, neutral note can prevent confusion.

Examples of invoice notes that often work well:

“Services were performed during the onboarding period at the request of the client project team. Please route to procurement/accounts payable for processing.”

“Per approval to begin work on [date], this invoice covers discovery and initial deliverables completed before vendor setup was finalized.”

“If a PO number is required, please advise and we can update the invoice accordingly.”

This language signals cooperation while making the timeline clear.

Practical obstacles: procurement, vendor systems, and “no PO, no pay”

Even when you have every right to invoice, enterprise payment systems can still block you. Understanding these obstacles helps you plan the fastest route to payment.

Vendor not in system: Accounts payable can’t pay a vendor that doesn’t exist in their database. Solve this by completing vendor registration quickly and asking your sponsor to flag the invoice as pending onboarding.

Missing purchase order: Many companies require a PO for any spend. If the work was urgent, they may be able to create a retroactive PO. Your sponsor needs to request it, because vendors often cannot.

Invoice date vs. service date mismatch: Some systems reject invoices where service dates precede contract dates, even if the business wants to pay. If possible, get the contract to include an “effective date” that covers the start of work. If that can’t happen, ask for a written exception approval from the appropriate manager.

Budget coding and approvals: If a department didn’t allocate budget yet, they may stall. Your detailed line items and clear value statement help your sponsor justify the expense.

The key insight: you’re not only invoicing the client; you’re also “invoicing the process.” Make the internal paperwork easy to complete.

Should you backdate the invoice date?

Generally, you should not backdate the invoice date to pretend it was issued earlier. Instead, use accurate dates: the invoice date should be the date you create the invoice, while the service period should reflect when work was performed.

Backdating can create accounting and trust issues. It can also complicate sales tax and reporting depending on the service and jurisdiction. The clean approach is transparency: “Invoice issued today for services performed earlier.”

Taxes and classification basics: W-9s, 1099s, and sales tax

Pre-onboarding invoicing often overlaps with tax paperwork. Here’s what typically comes up.

W-9 requests: US clients commonly ask independent contractors and vendors to complete a Form W-9 so they can report payments if required. Having this ready speeds up onboarding.

1099-NEC: Many businesses issue Form 1099-NEC for payments made to qualifying contractors. This is the client’s reporting responsibility, but they may need your tax information to do it correctly.

Sales tax: Sales tax on services varies widely by state and by service type. Some professional services are not taxed in many states, while certain digital products, SaaS, or specific service categories may be taxable in some jurisdictions. If sales tax applies to your service in the client’s location, invoice accordingly and remain consistent. If you’re unsure, consider obtaining guidance relevant to your situation before charging tax, because charging tax incorrectly can create issues for both you and the client.

These issues aren’t unique to pre-onboarding work, but onboarding delays often happen because tax forms are missing. Treat tax paperwork as part of your “get paid” workflow.

How to protect yourself next time: a simple pre-onboarding authorization step

If pre-onboarding work is common in your business, set up a lightweight “start-work authorization” practice that doesn’t slow momentum but does protect you. The goal is a written checkpoint that confirms three things: scope, pricing approach, and permission to begin.

A simple message can do the job:

“Confirming we’ll begin [scope] on [date] at [rate or fixed fee]. This work will be invoiced even if vendor onboarding is still in progress. Reply ‘approved’ to confirm.”

You’re not being difficult—you’re being clear. Most reasonable clients understand this, and the ones who resist may be signaling payment risk.

Using deposits or paid discovery to avoid pre-onboarding risk

Another way to reduce risk is to charge an upfront deposit or sell an initial “discovery” package that is easy to approve and pay. Deposits can align incentives: the client has skin in the game, and you’re not funding the project while waiting for procurement.

If you offer deposits, define how they apply:

Is the deposit credited against the first invoice? Is it non-refundable? What triggers the start of work? Having these terms in a short agreement or proposal helps prevent confusion.

For enterprise clients that can’t pay deposits easily, a small fixed-fee initial phase may be easier than open-ended hourly work. It gives procurement a clean spend approval.

What if the client refuses to pay because onboarding wasn’t complete?

If a client refuses to pay, don’t jump immediately to threats. Start by diagnosing the real reason. Often, “onboarding” is a convenient label for one of three issues: process blockage, scope confusion, or a decision-maker who didn’t expect the cost.

Here’s a practical escalation path:

Step 1: Clarify and document: Send a polite message summarizing what was delivered, when it was authorized, and the total amount due. Offer to provide supporting emails and deliverables.

Step 2: Ask for the internal path: “What does AP need to process this? Vendor setup, PO, approval?” Make them tell you the checklist.

Step 3: Engage your sponsor: The person benefiting from your work is usually the best ally. Ask them to help route the invoice internally.

Step 4: Offer an administrative workaround: For example, updating the invoice with a PO number once issued, splitting the invoice into milestones, or adjusting line items to match internal categories.

Step 5: Set a firm but professional deadline: If the client is stalling without explanation, communicate a clear due date and next steps (such as pausing further work). Keep the tone factual.

If the client still refuses, your options depend on the amount, your appetite for conflict, and your evidence. Small claims court, collections, or legal counsel may be considered for larger disputes, but many situations resolve once the right person approves the payment internally.

Can you keep working while onboarding is pending?

You can, but it’s a business decision. Continuing work without payment or formal setup increases your risk. If you decide to proceed, consider setting a cap: “We can continue up to X hours or through Y milestone while onboarding is finalized.” This keeps momentum without leaving you exposed.

In some cases, the safest approach is to pause until onboarding is complete. If the client truly needs the work, they will prioritize the paperwork.

How clients evaluate pre-onboarding invoices (and how to align with their expectations)

Clients typically ask internal questions like:

Who approved this spend?

Is the rate reasonable and within budget?

Did we receive what we’re being billed for?

Is there any compliance reason we can’t pay?

Will paying this invoice create a precedent that bypasses procurement?

Your invoice should help them answer these questions quickly. That’s why clarity beats cleverness. A clean, detailed invoice that maps directly to deliverables and dates is easier to approve than a vague invoice that forces internal debate.

Best practices for invoicing pre-onboarding work in a way that gets paid

Here are practical habits that consistently reduce friction:

Send a confirmation before starting: Even a brief email with “approved” is powerful.

Document work in real time: Keep time logs, meeting notes, and delivery records. You don’t need to overwhelm the client with details, but you should have them.

Invoice promptly: The longer you wait, the easier it is for someone to question the work or claim it wasn’t needed.

Use simple, consistent line items: For recurring services, use standardized descriptions so the client recognizes what they’re paying for.

Align with the client’s billing cadence: Some clients process invoices weekly, biweekly, or monthly. Sending your invoice right before their cutoff can reduce delays.

Route the invoice to the right place: Ask whether invoices should go to an AP inbox, procurement portal, or vendor management system.

Be prepared to reissue with a PO number: Many systems require it. Make this easy rather than treating it as an insult.

Pause work if payment risk increases: Protect your time and cash flow. A polite pause can motivate action.

How invoice24 can help you handle pre-onboarding invoices smoothly

When you’re billing for work completed before onboarding, professionalism and clarity do a lot of heavy lifting. A well-structured invoice with the right fields and clean line items can reduce internal friction and shorten the time from “we should pay this” to “this is paid.”

With invoice24, you can create invoices that clearly show service dates, detailed descriptions, and organized line items so your client’s finance team can approve the charge without back-and-forth. You can also reuse client details, standardize your service descriptions, and keep your invoicing consistent across projects. That consistency matters when procurement teams are scanning for anything that looks “off policy.”

If a client asks for changes—like adding a purchase order number or adjusting the phrasing of a line item—you can update and resend quickly without rebuilding the entire invoice. The less time you spend wrestling with formatting and admin, the more time you can spend doing billable work.

Sample invoice structure for pre-onboarding work

While every business is different, a strong pre-onboarding invoice often follows a familiar structure:

Header: Invoice number, invoice date, your business details, client details.

Service period: A clearly labeled range (dates worked).

Line items: Each with a description, quantity (hours or units), rate, and amount.

Notes: A short statement explaining that work was performed during onboarding at the client’s request and offering to add a PO if needed.

Payment terms: Due date, accepted payment methods, and any late fee policy if you use one.

This structure anticipates the questions that cause delays.

Red flags that suggest you should not start work before onboarding

Sometimes the best invoicing strategy is not to create the problem in the first place. Be cautious if you see these warning signs:

The client refuses to confirm scope or rates in writing.

They insist onboarding will take “a long time” without offering a workaround.

They won’t identify a specific person responsible for approvals.

They have a history of late payments or vendor disputes.

They ask for significant deliverables before any agreement, calling it “just a quick test,” without acknowledging it’s billable.

In these cases, push for a paid kickoff, a deposit, or a signed short-form agreement before you proceed.

Key takeaways

In the US, invoicing for work completed before formal onboarding is usually possible when the work was authorized and you can document what you delivered. The biggest risks are not always legal; they’re operational—procurement rules, PO requirements, and vendor system limitations that delay payment even when the client wants to pay.

Your best defense is a combination of clarity and process: get written approval to begin, keep records, invoice with detailed line items and service dates, and help your client route the invoice through their internal requirements. If onboarding delays are common, build a lightweight authorization step into your workflow and consider deposits or fixed-fee initial phases to protect your cash flow.

When you present pre-onboarding work professionally, you reduce friction, preserve the relationship, and get paid for the value you already created.