What Is an Invoice Number? How to Number Your Invoices (With Examples)

What is an invoice number?

An invoice number is a unique, sequential number that you assign to each of the invoices you send to clients. When used properly, invoice numbers make it easy to organize sent invoices, An invoice number is a sequential number that you assign to each of the invoices you send to clients. 

When used properly, invoice numbers make it easy to organize sent invoices, document your business revenue and income for taxes purposes, and track incoming and outstanding payments.

Every invoice number should be unique and clearly visible on each of your invoices. Here’s what you should know about invoice numbers:

• Invoice numbers are found at the top of the invoice
• They can be alphanumeric, including both letters and numbers (no special characters or symbols)
• They may also include a client’s name or initials
• They should be in order and never skip a number in the sequence
• They should be consistent for each client and/or project

Invoice numbers typically follow a basic numbering system, assigning a unique number to each invoice based on the invoice number format you choose.

In some states, including invoice numbers on your invoices is a legal requirement, so if you aren’t using them already, now’s a good time to start.READ MORE: How to make an invoice

Why are invoice numbers important?

Invoice numbers are beneficial to small business owners for many different reasons. Using a unique identifier for each new invoice can help you to:

1. Document your business revenue and income for tax and accounting purposes

With multiple jobs and clients to track each year, knowing how many clients you billed and how much income you received is a major task. Because invoice numbers are sequential, they show you how many invoices you’ve sent out in a given time period and for how much.

This is especially useful for your accountant and when tax time rolls around. You’ll know exactly how many jobs you did and how much they were for, which makes calculating your business revenue and income and tracking received payments a breeze.

READ MORE:Small business tax deductions to save money when filing

How to assign invoice numbers [examples]

You can assign invoice numbers in many different ways. Some examples of the most common invoice numbering formats are:

Sequentially

An invoice number example of this format would be 1001, 1002, 1003, 1004, etc. It’s best practice to use three to four (or more) digits—like 1001 instead of 1—to avoid confusion as your business grows and you bring on more clients and jobs.

Chronologically

Chronological invoice numbering typically includes the date as well as a unique invoice number so that not all invoices from the same day end up with the same number. For example, 20240724-1001, 20240724-1002, etc.

By client number

You can assign an individual number to each of your clients and use it as part of your invoice number. Let’s say you have a client business named John Smith Landscaping who is client number 49. A client number-based system would look like this: 49-1001, 49-1002, etc.

By project number

Similar to a client number, project numbers are unique numbers assigned to specific projects. If you were numbering a project as 299, your invoices associated with it could be 299-1001, 299-1002, etc.

Names and numbers

You can also mix client names and numbers. For example, if you’re working on a project for John Smith Landscaping, you can create a custom alphanumeric identifier to use at the front of the invoice number, such as JSL-1001, JSL-1002 and so on.

READ MORE: Master the art of invoicing with these invoicing basics

While there are no hard and fast rules when it comes to invoicing, using a sequential (or consecutive) invoice numbering system is the easiest way to keep invoices organized and works best for avoiding duplicate invoice numbers and typos.

Regardless of which method you use, it’s best to avoid generic terms that may not be specific to particular clients in your invoice numbers.

For example, if you’re working on jobs or projects for different landscaping companies, an invoice number like Mow1001 could be the same for multiple invoices across different customers.

And if you ever decide to change the format of your invoice numbers, it’s best to wait until a new accounting cycle to avoid any confusion in the tracking of invoices and payments.

Invoice number tracking: How to make invoice numbers

Regardless of whether you’re using invoicing software or an invoice template that you update Regardless of whether you’re using invoicing software or an invoice template that you update manually for each client, follow these best practices to improve your results:

• Make sure invoice numbers are easy to see and identify on each invoice
• Keep a digital record of each invoice you send (ideally in a PDF format)
• Pick a numbering method and stick with it to ensure consistency

Jobber’s field service invoice software is an effective and efficient tool to create, store, and automate invoices. Not only will it reduce your margin for error, but it will make creating, sending, and tracking invoices faster and easier.

And, the more quickly you can roll out invoices, the more likely you are to get paid on time and in full.

How to fix an invoice number error

Every so often you’re going to run into a mistake with your invoice number, whether it’s a duplicate invoice number or you’ve used the wrong client or project identifier, but it’s never too late to update the documentation between you and a client.

If you’ve sent an invoice with an incorrect number and your client hasn’t paid yet, you can always send the corrected invoice and let your client know they can expect a new document to review and complete.

If the client has already paid the outstanding invoice, you still need to send the updated invoice for review, however you should also get in writing that your client understands the payment will be applied to the corrected invoice number. 

For more strict clients, you will need to cancel the payment, issue a refund, provide the corrected invoice and request payment again.

What to put on an invoice

There are key pieces to writing a clear and concise invoice that help you track all the important information about a client, a job or project, and the payment method and terms.

Your invoice should include:

• Invoice date
• Invoice number
• Your business information: Contact name, company name, address, phone number, email
• Your client information: Contact name, company name, address, phone number, email
• Purchase order (PO) number
• Product and/or service description including quantities and price
• Delivery dates for products or services
• Deposits made by client
• Subtotal
• Taxes
• Grand total
• Payment terms and payment due date
• Payment method options