Invoice Number Generator
Generate sequential invoice numbers for your business. Create invoice number formats with prefix, year, and sequence.
About this generator
A clean invoice number system saves hours at tax time. This tool generates a sequence of invoice numbers in the format you choose: a prefix, a separator, an optional year or financial year, a starting number and a number of digits. Copy the list and paste it into your accounting software or tracker.
Sequential, unique numbers are a requirement under GST for each financial year and a good habit everywhere else. The financial-year formats, such as 25-26, help you keep different years apart without resetting the count by hand.
How to use it
- Enter a Prefix, such as INV.
- Choose a Separator: dash, slash, underscore or none.
- Choose a Year format, including financial years like 25-26.
- Set the Starting Number, the number of Digits and how many numbers to generate.
- Press Generate Invoice Numbers, then Copy All.
Number format
Each invoice number is built as Prefix + Separator + Year + Separator + Number, with the number padded to the digits you pick. For example, prefix INV, separator slash, year 25-26, start 1 and 4 digits gives INV/25-26/0001, then INV/25-26/0002 and so on.
Worked example
Prefix INV, separator dash, year 25-26, start 1, 4 digits
| First number | INV-25-26-0001 |
| Second number | INV-25-26-0002 |
| Tenth number | INV-25-26-0010 |
Restart the count at 0001 when a new financial year begins, which is why the year is part of the number.
Tips and common mistakes
- GST rules require invoice numbers to be unique within a financial year, up to 16 characters, using letters, digits, hyphen and slash only.
- Use a separate series for credit notes, such as CN, so they do not interrupt the invoice sequence.
- Do not skip or reuse numbers. If an invoice is cancelled, keep it on file marked as cancelled.
- Use enough digits for a year of invoices so that sorting works. Four digits is enough for most small businesses.
- Keep the format the same across the year. Changing it mid-year confuses auditors.
Frequently asked questions
What should an invoice number look like?
A unique, sequential identifier, usually with a prefix and a year, such as INV/25-26/0001.
Are there GST rules on invoice numbers?
Yes. They must be unique for the financial year, no more than 16 characters, and use only letters, digits, hyphen and slash.
Should I restart numbering each year?
Under GST you can restart each financial year, which is why the year is often part of the number.
Can I use my own prefix?
Yes. Use a short prefix that identifies your business or document type.
What if I cancel an invoice?
Keep the number on record as cancelled. Do not reuse it.
How many digits should I use?
Four digits gives you 9,999 invoices a year, which suits most small businesses.