How to use the Invoice Number Sequence Checker
- Paste invoice numbers, one per line, or choose a TXT, CSV or TSV file. For a table, pick the column with the invoice numbers.
- Select Check sequence.
- Review the missing ranges, duplicates and unreadable numbers, and download the report as CSV.
Supported files and limits
- The text before the last group of digits identifies the series: INV-2026-0042 belongs to the series INV-2026-. A series column in a table separates the numbers further.
- Gaps are found between the lowest and highest number in each series. Numbers missing before the first or after the last cannot be detected.
- Numbers are compared exactly: spaces, letter case and leading zeros count, except that 0042 and 42 are treated as the same number.
- A gap or duplicate is a finding to review, not a legal or tax conclusion. Up to 50,000 numbers or 10 MB.
Common questions
Do invoice numbers have to be consecutive?
Many countries require a continuous, unique sequence, for example under the EU VAT rules for invoice numbering, though one or more separate series are usually allowed. Check the rules that apply to you with your accountant.
Can I check credit notes and invoices together?
Yes. Numbers with different prefixes, such as INV- and CN-, are grouped into separate series automatically.
What does "No number at the end" mean?
The value does not end in digits, for example DRAFT or an empty cell, so it cannot be placed in a sequence. It is listed so nothing is skipped silently.
Are my invoice numbers uploaded?
No. The check runs in your browser, and nothing is sent to our server or anyone else.