An invoice number is the unique, identifying number that you assign to an invoice so you can track transactions and payments. An invoice number is also known as an invoice ID. Invoice numbers should contain only numbers, only letters, or a combination of both.
Invoice numbers are an extremely important part of an invoice because they identify a specific purchase with its corresponding payment from the client or customer.
How do I assign invoice numbers?
You can assign invoice numbers to your invoices in multiple ways. Regardless of the numbering method, it’s important to make every invoice number unique. Generally, contractors and small businesses will number invoices sequentially or chronologically.
- Sequentially: If you choose to number invoices sequentially, assign your first invoice with a number, such as 1000000. The next invoice’s number would then follow in the numerical sequence. In this case, the next invoice number would be 1000001.
- Chronologically: If you choose to number invoices chronologically, insert an invoice’s date into the invoice number along with a sequential number. For example, if you made an invoice for a customer on September 5, 2021, the invoice number could be 20210905-01.
Additionally, you may choose to include an assigned customer number at the beginning of an invoice number and separate it by a hyphen. Including a customer number can help you easily identify invoices for your different customers.
You may include letters in an invoice number to help you further organize and identify customers, orders, and projects.