How To Create Custom Invoice Numbers In WooCommerce?

In this blog post, learn how to create and customize your WooCommerce invoice numbers. We’ll walk you through setting up a WooCommerce custom invoice number format using prefixes, suffixes, and custom sequences for better organization and branding.

Invoice numbers serve as unique identifiers for each transaction in your store, similar to WooCommerce order numbers, helping you track invoices for received orders. However, a random sequence of invoice numbers can cause confusion.

Creating a custom sequence of invoice numbers is essential for maintaining organized financial records, ensuring businesses can easily access transaction details when needed.

This article will help you create custom invoice numbers for WooCommerce invoices.

Let’s get started.

An invoice number is a unique identifier assigned to each invoice issued for a transaction. Think of it like a digital fingerprint for every invoice—no two should be the same.

It helps businesses and customers track invoices of orders, making it easier to manage records, payments, and accounting. Using clear and structured invoice numbers ensures accurate record-keeping and simplifies the retrieval of transaction details when needed.

Invoice numbers play a crucial role in business operations for several reasons:

• Unique identification: Invoice numbers are unique identifier so it can be used to easily identify invoices of purchases. It simplifies the bookkeeping process and facilitates easy retrieval of information.
• Simple payment tracking: If a business maintains a sequential numbering system, it will be simple for customers to locate an old invoice if any issues arise. Otherwise, both the buyer and the seller may have to spend a lot of time and effort locating it.
• Avoid making duplicate payments: A structured invoice numbering system helps prevent errors and duplication. Incorrect bills can cost your company a lot of time, money, and reputation as well. By having distinct invoice numbers, businesses can avoid confusion and maintain the integrity of financial records.
• Legal compliance: Many countries have laws that mandates the requirement of having a proper invoice numbering system. Invoice numbers provide essential information for tax regulations and auditing purposes.
• Offer a reputable and professional service: Even if there is no legal requirement to include invoice numbers in your location, customers expect them as reference numbers for transparency. It also showcase your professionalism.
• Streamlines Workflow: Whether you’re integrating with accounting tools, generating reports, or syncing with third-party systems, a well-structured invoice number ensures everything runs smoothly behind the scenes.

Example of a Structured Invoice Number

A good invoice number might look like this:

INV-2025-0456

Here:

• “INV” is a prefix to indicate that it’s an invoice.
• “2025” shows the year of the transaction.
• “0456” is the sequential number for that invoice.

This kind of format is easy to understand at a glance, and it scales well as your business grows.

Follow the below steps to create and customize invoice numbers for WooCommerce Invoices:

Step 1: Install WebToffee WooCommerce PDF Invoices Plugin

To create custom invoice numbers in WooCommerce, you can install the WebToffee WooCommerce PDF Invoices Plugin.

• From the dashboard, navigate to Plugins > Add New.
• Search for the keyword ‘PDF invoices’ and identify the WebToffee plugin.
• You can then install and activate it.

Step 2: Customize Invoice Settings

Navigate to Invoice/Packing > Invoice from your WordPress dashboard.

Here, you will find a set of features essential to set up a fully functional and professional WooCommerce invoice. 

Read the article on how to set up a PDF invoice to know more.

Step 3: Create Custom Invoice Numbers In WooCommerce

You will find the options to personalize your WooCommerce invoice number on the General page of the tab Invoices.

You can create a unique invoice number using a custom prefix, suffix, or number series, or you can even mirror the order number as the invoice number.

• Select Custom number from the Invoice number format dropdown to define your custom invoice number series.
• Next, enter your desired starting number in the Invoice starting number field to begin the custom invoice sequence. For example, if you enter 5, the next invoice generated will have the invoice number 5, the one after that will have 6, and so on. 
• Add a prefix and/or suffix to your invoice number using the designated fields. Leave the fields blank if you do not wish to include a prefix or suffix. To add a date format as the suffix, click the Suffix field and select a format from the dropdown menu.
• Now, enter the total length of your preferred invoice number string, padded with zeros. For instance, enter an invoice number with a length of 7 and an initial number of 8091. Then the freshly created number, padded with three zeros, will be 0008091.
• After the necessary changes, click the Update Settings button.

For example, say the prefix is SC, and the suffix is the UK.

Using the above configuration, let’s look at the invoice number before and after resetting the invoice number.

Before

After

When it comes to setting up your WooCommerce invoice numbers, it’s tempting to go with something quick and simple—but a well-thought-out format can save you a lot of confusion and effort down the road.

Here are some proven best practices to follow when creating invoice numbers:

1. Avoid Exposing Internal Order Structure

It’s common to base invoice numbers directly on WooCommerce order IDs, but doing so may reveal internal business data or lead to security concerns. For example, sequential order IDs could hint at your total order volume, which might be sensitive information for competitive reasons.

Tip: Add a prefix, suffix, or additional sequence layer to mask the actual order ID. Instead of just #1245, use something like INV-2025-045.

2. Ensure Uniqueness

Each invoice number must be completely unique. Repeating numbers across different transactions can cause accounting discrepancies, payment tracking errors, or even tax reporting issues.

• Most plugins, like WebToffee’s PDF Invoices, auto-increment invoice numbers to avoid duplicates.
• If you’re resetting invoice numbers periodically (monthly or yearly), make sure to include the month/year in the format to preserve uniqueness.
  

3. Consider Future Scalability

Your invoice number format should support growth. Today, you might be issuing 10 invoices a day—but what if that becomes 100 or more?

Avoid formats that limit you, like INV-01, which can become confusing or unusable very quickly. Instead, use padded numbers such as:

INV-2025-0001

This ensures your numbering remains consistent and tidy even as volume increases.

4. Keep Format Human-Readable

Clarity is key. You and your customers should be able to understand what an invoice number refers to without digging through a manual.

Use:

• Clear prefixes (INV, WC, or your store initials)
• Year or month references (2025, 0525)
• Sequential numbers with zero padding (0012, not just 12)
  

Avoid:

• Random alphanumeric strings (XZ78L2), unless required for system reasons
• Unstructured formats like long chains of numbers without separators
  

5. Document Your Format for Your Team or Accountant

If your invoice numbering format includes resets, changes over time, or has special logic behind it, make sure to document it. This is especially important if:

• You have multiple team members handling invoices
• You integrate with accounting software or external services
• You plan to migrate systems later
  

This documentation can be a simple one-pager explaining:

• The format logic
• When numbers reset (if applicable)
• Where the invoice numbers are generated (e.g., plugin settings)
  

Having this clarity helps avoid misunderstandings and makes onboarding or audits a lot easier.

In addition to the free variation, the WooCommerce invoice plugin is also available in a premium variation. Some of the key features of the premium plugin include,

• Auto-generate invoices, packing slips, and credit notes
• Show payment links on the invoice
• Add ‘Pay Later’ option at checkout
• Attach documents to selected order status emails
• Enable customers to print invoices & packing slips
• Customize document layout & properties
• Show product variation data
• Add custom data to documents
• Multiple display options for bundle products
• Group products by ‘Category’

Keeping your invoice numbers accurate and in order is super important for clear records and smooth transactions. In this post, we talked about why invoice numbers matter and how they help your online business stay organized.

By following the steps we shared, WooCommerce store owners can easily fix any issues with invoice numbers and keep everything running smoothly. It’s also a good idea to check your invoice numbers regularly so you can catch any problems early.

If you’re looking to set up a WooCommerce custom invoice number format that fits your business, the WooCommerce PDF Invoices and Packing Slips plugin makes it easy. It helps you save time, cut down on manual work, and stay on top of your invoicing.

Thanks for reading, and happy invoicing!