Invoice Number Generator
Invoice Number Generator is a free business tool that runs directly in your browser with no account required.
About this tool
This tool designs a complete invoice numbering scheme rather than just spitting out one number. Combine a prefix, client code, and date stamp with a zero-padded sequence, optionally append a Mod 10 check digit, and choose a reset rule (never, monthly, yearly, or per client). It previews a batch of numbers with their successors, generates written policy notes in Markdown, and exports both a CSV and the policy document.
How to use
- Enter a Prefix (like INV) and an optional Client code.
- Set the starting Sequence, Number padding width, and how many numbers to preview with Generate count.
- Pick a Separator, Date format, Reset rule, and whether to append a Mod 10 Check digit.
- Copy the current invoice number, review the pattern and period key, and use the download buttons for the numbers CSV and policy notes.
Frequently asked questions
What does the reset rule change?
It defines when your sequence restarts: never (one continuous series), monthly, yearly, or a separate series per client. The result shows a period key — like a year-month stamp or client tag — that identifies which counter each number belongs to.
How is the Mod 10 check digit computed?
All digits in the assembled number are weighted alternately by 3 and 1, summed, and the digit that rounds the sum up to a multiple of 10 is appended. It lets you catch most typos when a number is keyed in manually.
What are the input limits?
Padding runs from 1 to 12 digits, the preview generates up to 100 numbers, and prefix and client codes are normalized to URL-safe characters.
What do the two downloads contain?
The CSV lists each generated number with its successor, period key, reset rule, and check-digit setting; the Markdown file is a written numbering policy with the pattern and operational notes you can drop into your team docs.
Can I reuse a voided invoice number?
Generally no — most accounting practices require gaps to stay documented rather than refilled, and the generated policy notes call this out explicitly.
Are my client codes or sequences stored?
No. Everything is generated in your browser on the fly and nothing is transmitted or persisted.