📋 Overview: B2B Unpaid Invoices

When a business client fails to pay for goods or services you provided, California law gives you powerful tools to collect what you are owed. A well-crafted demand letter is often the first step to recovering payment without costly litigation.

When to Use This Guide

This guide is for business-to-business (B2B) invoice collection when:

💰 Invoice is Past Due

The payment deadline stated on your invoice has passed without payment

📩 No Response

The debtor has ignored your payment reminders or informal collection attempts

👥 B2B Transaction

Both you and the debtor are businesses (not consumer debt)

✅ Work Completed

You fully performed your obligations - goods delivered or services rendered

Common B2B Invoice Dispute Scenarios

💼 Services Rendered But Not Paid

▼

You provided professional services (consulting, marketing, IT, legal, accounting, etc.) and the client accepted the work but has not paid the invoice. This is the most common B2B collection scenario. Your demand should emphasize completion of the work and acceptance by the client.

📦 Goods Delivered But Not Paid

▼

You sold and delivered goods to a business customer who has not paid. California Commercial Code provisions apply to sales of goods. Document delivery confirmation, acceptance of goods, and any inspection period that has passed without rejection.

💲 Partial Payment Received

▼

The client made a partial payment but owes a remaining balance. Your demand should acknowledge the partial payment, state the exact remaining balance, and demand full payment of the outstanding amount plus any applicable late fees and interest.

🔁 Ongoing Relationship with Outstanding Balance

▼

You have an ongoing business relationship with multiple invoices, some of which remain unpaid. Your demand should itemize all outstanding invoices, indicate which are past due, and consider whether to continue providing services while collection is pending.

👍 What You Can Recover

  • Principal amount - The full invoice amount owed
  • Prejudgment interest - 10% per year on the unpaid amount (Cal. Civ. Code 3287)
  • Late fees - If specified in your contract or invoice terms
  • Attorney fees - If your contract includes an attorney fee provision (Cal. Civ. Code 1717)
  • Collection costs - If specified in your contract

⚠ Statute of Limitations

California has strict time limits for filing unpaid invoice claims:

  • Written contracts: 4 years from the date payment was due (CCP 337)
  • Oral contracts: 2 years from the date payment was due (CCP 339)
  • Open book accounts: 4 years from the last item in the account (CCP 337)

Do not delay - act quickly to preserve your rights and maximize interest recovery.

💰 Calculate Your Damages

Under California law, you can recover the full invoice amount plus interest and other costs. Here is how to calculate your total claim.

Damage Type Description
Principal Amount The total unpaid invoice amount for goods delivered or services rendered.
Prejudgment Interest (10%) Under Cal. Civ. Code 3287(a), 10% per year calculated from the date each invoice was due until payment. Interest accrues daily.
Contractual Late Fees If your contract or invoice terms specify late fees (e.g., 1.5% per month), these are recoverable if they are a reasonable estimate of actual damages.
Attorney Fees Under Cal. Civ. Code 1717, recoverable if your contract contains an attorney fee provision. The prevailing party gets fees.
Collection Costs If your contract provides for recovery of collection costs, you can include documented collection expenses.

📊 Sample Damages Calculation

Example: Consulting Services Invoice - 18 Months Overdue

Original invoice amount $45,000.00
Prejudgment interest (10% x 1.5 years) $6,750.00
Contractual late fees (if applicable) $2,025.00
Estimated attorney fees (if contract provides) $5,000.00
TOTAL DEMAND $58,775.00

Calculating Prejudgment Interest

The formula for calculating prejudgment interest is:

🔎 Interest Calculation Formula

Principal x 0.10 x (Days Past Due / 365) = Prejudgment Interest

Example: $50,000 invoice, 547 days overdue
$50,000 x 0.10 x (547 / 365) = $7,493.15 in interest

⚠ Late Fees vs. Prejudgment Interest

If your contract specifies late fees (e.g., 1.5% per month = 18% annually), you generally must choose between contractual late fees OR statutory prejudgment interest - you cannot recover both on the same amount. Calculate which is higher and demand that amount.

✅ Evidence Checklist

Gather these documents before sending your demand letter. Strong documentation increases your leverage and supports litigation if needed.

📄 Contract Documents

  • ✓ Signed service agreement, sales contract, or master agreement
  • ✓ Purchase orders or work orders
  • ✓ Statements of work or project scopes
  • ✓ Terms and conditions (if referenced in contract)

📋 Invoices

  • ✓ All unpaid invoices with dates and amounts
  • ✓ Invoice delivery confirmation (email receipts)
  • ✓ Payment terms stated on each invoice
  • ✓ Partial payment records (if applicable)

📦 Delivery Confirmations

  • ✓ Signed delivery receipts or bills of lading
  • ✓ Shipping tracking confirmations
  • ✓ Service completion sign-offs
  • ✓ Client approval emails or acceptance documentation

📩 Communications

  • ✓ Email correspondence about the project/order
  • ✓ Payment reminder emails sent
  • ✓ Any promises to pay or payment plans discussed
  • ✓ Any disputes or complaints raised (and your responses)

🔒 Documentation Best Practices

  • Keep all originals in a safe location
  • Create a chronological timeline of the business relationship
  • Save all emails in PDF format with headers showing delivery
  • Calculate a running total of principal + interest through the current date

📝 Sample Language

Copy and customize these paragraphs for different unpaid invoice scenarios.

Services Rendered Scenario

Services Rendered - Opening
I am writing on behalf of [YOUR COMPANY] to formally demand payment for professional services rendered to [DEBTOR COMPANY]. Despite our satisfactory completion of all contracted work and your acceptance of our services, Invoice No. [INVOICE NUMBER] dated [INVOICE DATE] in the amount of $[AMOUNT] remains unpaid. This invoice was due on [DUE DATE] and is now [NUMBER] days past due.

Goods Delivered Scenario

Goods Delivered - Opening
This letter constitutes a formal demand for payment on behalf of [YOUR COMPANY]. On [DELIVERY DATE], we delivered [DESCRIPTION OF GOODS] to [DEBTOR COMPANY] pursuant to Purchase Order No. [PO NUMBER]. Your company accepted delivery of these goods, and the inspection period has passed without rejection. Invoice No. [INVOICE NUMBER] in the amount of $[AMOUNT] was due on [DUE DATE] and remains unpaid. Under California Commercial Code Section 2607, you are obligated to pay for goods accepted.

Partial Payment Scenario

Partial Payment - Opening
This letter demands immediate payment of the outstanding balance owed by [DEBTOR COMPANY] to [YOUR COMPANY]. While we acknowledge receipt of your partial payment of $[PARTIAL PAYMENT AMOUNT] on [PAYMENT DATE], a balance of $[REMAINING BALANCE] remains unpaid on Invoice No. [INVOICE NUMBER]. This remaining balance has been outstanding since [ORIGINAL DUE DATE]. We demand immediate payment of the full remaining balance plus accrued interest.

Ongoing Relationship Scenario

Ongoing Relationship - Opening
Despite our valued ongoing business relationship, [DEBTOR COMPANY] has allowed multiple invoices to become significantly past due. As of [CURRENT DATE], the following invoices from [YOUR COMPANY] remain unpaid: Invoice No. [INVOICE 1] dated [DATE] for $[AMOUNT]; Invoice No. [INVOICE 2] dated [DATE] for $[AMOUNT]. The total outstanding balance is $[TOTAL]. We must receive payment before we can continue providing services.

Legal Basis Paragraph (Use for All Scenarios)

Legal Basis - California Law
Under California Civil Code Section 3287(a), we are entitled to prejudgment interest at the rate of 10% per annum on the outstanding balance, calculated from the date each invoice became due. Additionally, pursuant to California Civil Code Section 1717 and the attorney fee provision in our agreement, we are entitled to recover reasonable attorney fees and costs incurred in collecting this debt. If litigation becomes necessary, we will seek the full amount owed plus all accrued interest, attorney fees, and court costs.

Demand and Deadline Paragraph

Demand and Deadline
DEMAND IS HEREBY MADE for payment of the total amount of $[TOTAL WITH INTEREST], consisting of $[PRINCIPAL] in principal and $[INTEREST] in accrued prejudgment interest through [DATE]. This amount must be received by [YOUR COMPANY] no later than [DEADLINE DATE - typically 10-15 days]. Payment should be made payable to [YOUR COMPANY] and sent to [PAYMENT ADDRESS]. Alternatively, payment may be wired to [BANK DETAILS IF APPLICABLE].

Consequences Paragraph

Consequences of Non-Payment
If we do not receive full payment by [DEADLINE DATE], we will have no alternative but to pursue all available legal remedies without further notice. This will include filing a lawsuit in the appropriate California court, where we will seek the full principal amount, all accrued and continuing prejudgment interest, reasonable attorney fees, court costs, and any other relief to which we are entitled. A judgment against [DEBTOR COMPANY] will become a matter of public record and may be reported to credit agencies. We strongly encourage you to resolve this matter now to avoid these consequences.

📄 Full Sample Demand Letter

Below is a complete demand letter template. Replace all [PLACEHOLDERS] with your specific information.

Complete Demand Letter Template
[YOUR COMPANY NAME]
[YOUR STREET ADDRESS]
[CITY, STATE ZIP]
[PHONE NUMBER]
[EMAIL ADDRESS]

[DATE]
VIA CERTIFIED MAIL, RETURN RECEIPT REQUESTED
AND EMAIL

[DEBTOR COMPANY NAME]
[ATTENTION: ACCOUNTS PAYABLE / CEO NAME]
[DEBTOR STREET ADDRESS]
[CITY, STATE ZIP]
Re: FORMAL DEMAND FOR PAYMENT
Invoice No(s): [INVOICE NUMBER(S)]
Amount Due: $[TOTAL AMOUNT DUE]

Dear [RECIPIENT NAME OR "Sir/Madam"]:

This letter constitutes a formal demand for payment on behalf of [YOUR COMPANY NAME] ("Creditor"). Despite repeated informal requests, [DEBTOR COMPANY NAME] ("Debtor") has failed to pay for [goods delivered / services rendered] as agreed.

BACKGROUND

On or about [DATE OF AGREEMENT/ORDER], Debtor engaged Creditor to provide [DESCRIPTION OF GOODS OR SERVICES] pursuant to [CONTRACT/PURCHASE ORDER/AGREEMENT REFERENCE]. Creditor fully performed its obligations, including [BRIEF DESCRIPTION OF PERFORMANCE]. Debtor accepted [the goods / the completed work] without objection.

Creditor issued the following invoice(s) to Debtor:

Invoice No. [INVOICE NUMBER], dated [INVOICE DATE], for $[AMOUNT], due [DUE DATE]
[ADD ADDITIONAL INVOICES IF APPLICABLE]

Despite the passage of the payment deadline and our subsequent payment reminders on [DATES OF REMINDERS], the total amount of $[PRINCIPAL AMOUNT] remains unpaid as of the date of this letter.

LEGAL BASIS FOR THIS DEMAND

Under California law, Debtor is obligated to pay for [goods accepted (Cal. Com. Code Section 2607) / services rendered]. California Civil Code Section 3287(a) entitles Creditor to prejudgment interest at the legal rate of 10% per annum on all sums due, calculated from the date each invoice became due. [IF APPLICABLE: Furthermore, pursuant to California Civil Code Section 1717 and the attorney fee provision contained in our agreement, Creditor is entitled to recover all reasonable attorney fees and collection costs incurred in pursuing this debt.]

AMOUNT DUE

As of [CURRENT DATE], Debtor owes the following:

Principal (unpaid invoices): $[PRINCIPAL AMOUNT]
Prejudgment interest (10% per annum through [DATE]): $[INTEREST AMOUNT]
[IF APPLICABLE: Late fees per contract: $[AMOUNT]]
TOTAL AMOUNT DUE: $[TOTAL]

Interest continues to accrue at the rate of $[DAILY INTEREST AMOUNT] per day until payment is received.

DEMAND

DEMAND IS HEREBY MADE that Debtor pay the total sum of $[TOTAL AMOUNT] within fifteen (15) days of the date of this letter, no later than [DEADLINE DATE].

Payment should be made by check payable to "[YOUR COMPANY NAME]" and mailed to the address above, or by wire transfer to:

Bank: [BANK NAME]
Account Name: [ACCOUNT NAME]
Account Number: [ACCOUNT NUMBER]
Routing Number: [ROUTING NUMBER]

CONSEQUENCES OF NON-PAYMENT

If Creditor does not receive full payment by [DEADLINE DATE], we will pursue all available legal remedies without further notice. This will include filing a lawsuit in the appropriate California court seeking:

  • The full principal amount owed
  • All accrued and continuing prejudgment interest
  • Reasonable attorney fees and costs
  • Court costs and filing fees
  • Any other relief the court deems appropriate

A judgment will become a matter of public record and may be reported to commercial credit reporting agencies, which could affect Debtor's ability to obtain credit and conduct business.

We trust this matter can be resolved without litigation. However, we are prepared to take all necessary legal action to protect Creditor's rights. Please contact the undersigned immediately to arrange payment or to discuss a resolution.

This letter is not intended to be a complete statement of all claims, damages, or legal theories available to Creditor, all of which are expressly reserved.

Sincerely,




[YOUR NAME]
[YOUR TITLE]
[YOUR COMPANY NAME]


Enclosures:
- Copy of Invoice(s)
- Copy of Contract/Purchase Order
- Proof of Delivery/Completion

💌 Sending Tips

  • Certified Mail: Always send via USPS Certified Mail with Return Receipt Requested to prove delivery
  • Email Backup: Also send by email to the primary contact and accounts payable to ensure receipt
  • Keep Copies: Retain copies of the letter and all enclosures for your records
  • Track the Deadline: Mark your calendar for the response deadline and follow up promptly if no payment is received

🚀 Next Steps

What to do after sending your demand letter.

Expected Timeline

Days 1-3

Debtor receives and reviews your demand letter

Days 3-10

Debtor consults with management, reviews their records

Days 10-15

Response expected: payment, payment plan offer, or dispute

If They Pay

Verify the payment covers principal plus interest through the payment date. If the payment is short, send a brief letter acknowledging receipt and demanding the remaining balance.

If They Offer a Payment Plan

Consider whether to accept. If you agree to a payment plan, document it in writing with clear terms including: payment amounts, due dates, consequences of default, and whether interest continues to accrue. Consider requiring a personal guaranty from the business owner.

If They Dispute the Debt

Review their claimed defenses carefully. Common defenses include claims of defective work, failure to deliver, or disputes about contract terms. Gather your evidence and consult with an attorney about the strength of their defenses versus your claims.

If They Don't Respond

  1. Small Claims Court (Up to $12,500)

    For claims up to $12,500 (increased from $10,000 in 2024), California Small Claims Court offers a fast, inexpensive option. No attorneys allowed, but you can represent your business. Filing fee is typically $75-$100.

  2. Limited Civil Court ($12,501 - $25,000)

    For claims between $12,501 and $25,000, file in California Superior Court, Limited Civil division. Simpler procedures than unlimited civil.

  3. Unlimited Civil Court (Over $25,000)

    For larger claims, file in Superior Court Unlimited Civil. Consider hiring a commercial litigation attorney. Many work on contingency or hybrid fee arrangements for strong collection cases.

  4. Collection Agency

    If litigation is not practical, consider assigning the debt to a commercial collection agency. They typically charge 25-50% of amounts recovered but handle all collection efforts.

⚠ Watch the Statute of Limitations

  • Written contracts: 4 years from when payment was due (CCP 337)
  • Oral contracts: 2 years from when payment was due (CCP 339)

A demand letter does NOT toll (pause) the statute of limitations. If your deadline is approaching, file suit immediately to preserve your rights.

Need Legal Help?

Complex collection matters or large claims often benefit from professional legal guidance. Get a 30-minute strategy call with an attorney to evaluate your case and options.

Book Consultation - $125

California Resources