An invoice number is a unique, sequential code that is systematically assigned lớn invoices.
Invoice numbers are one of the most important aspects of invoicing as they ensure that income is properly documented for tax and accounting purposes. They also make it easier lớn track payments and manage overdue invoices.
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Each invoice issued should be assigned a unique invoice number. The invoice number should always be clearly stated on the invoice – without an invoice number, an invoice is not considered a legal document.
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As proforma invoices are not ‘true’ invoices, they shouldn’t be assigned invoice numbers.
How lớn assign invoice numbers
Invoice numbers are a mandatory invoice field. They should be assigned sequentially, meaning that the number of each new invoice increases. Legally, an invoice number sequence should never contain repeats or gaps.
It’s not recommended lớn simply number invoices '1', '2', '3', etc. as this can be confusing when invoice numbers reach double or triple figures. New businesses may not have high numbers of invoices lớn begin with, but it’s important lớn consider future growth when choosing an effective invoice numbering system.
A common way lớn create a longer, more specific invoice number is lớn include the month or year the invoice was issued.
For example, within a sequence that refers lớn the year, the first invoice in 2021 could be numbered '210001'. The next invoices would be '210002', '210003' and ví on. At the start of a new year, the numbers would be reset. The first invoice number of 2022 would be '220001'.
This system allows you lớn quickly see which year an invoice is issued and still follows the sequential numbering requirement.
Alphanumeric invoice numbers
An invoice number doesn’t always contain just numbers – it’s also possible lớn create a unique code that includes numbers, letters, and special characters such as slashes (/) or dashes (-).
Adding letters and characters lớn an invoice number series can help make it easier lớn organise records and identify invoices.
An alphanumeric invoice number series must follow the same rules as regular invoice numbers series – they should be sequential and should never contain gaps.
Letters can be used lớn identify different types of documents, lượt thích quotes and delivery notes. For example, an invoice number sequence could contain 'INV' and a quotation number sequence could contain 'QUT'. If you choose lớn include letters in your invoice number series, the letters should not be changed – only numbers should increase.
Examples of alphanumeric invoice sequences include:
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2018/INV/0001
18-QUT-0001
2018/0001
2018-0001
18/0001
When lớn update invoice numbers
If you use an invoice number series that follows the date, it should be updated accordingly. For example, the invoice number 'INV-21-12-009' includes the month and year, referring lớn the ninth invoice issued in December 2021. The first invoice of the next month, January 2022, would be numbered 'INV-22-01-001'.
If you want lớn change your invoice number series entirely, it’s best lớn wait until the next accounting period as this helps avoid confusion and prevents missing or duplicate invoice numbers.
However, if you change your invoice number series, you should be sure that you don’t repeat or exclude any numbers. This means that if your last invoice number was ‘023’, your next invoice number must include '024' – for example '21/INV/024' or '2021-024'.
Invoice numbers and deleted invoices
As a standard rule, invoices should not be deleted. Because invoices are numbered sequentially, an invoice that has been completed in your records and is then deleted could show up as a gap in your financial records.
If you want lớn remove a transaction, it’s usually better lớn issue a credit note for the same amount. This will effectively cancel out the invoice while ensuring that your number sequence is complete.
Invoice numbers with SumUp Invoices
With SumUp Invoices, it’s easy lớn keep track of your invoice numbers.
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Use our mặc định numbering system, or choose your own custom invoice number series by typing your preferred number into the ‘Invoice No.’ box. The number will automatically be updated lớn the following sequential number whenever you create a new invoice.
You can also create unlimited quotes and assign a quote numbering list. The system uses machine learning lớn automatically detect and assign the next number in the sequence.
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