Invoice Number Generator
Generate a batch of sequential invoice numbers with a consistent prefix and digit format — useful for setting up a numbering system before your first invoice, or picking up a consistent sequence after switching tools.
The calculation, explained
Each number combines your prefix with the starting number, incrementing by 1, padded to your chosen digit count (e.g. digit count 4 turns “7” into “0007”). A consistent format makes your invoices easier to sort and search later.
Invoice numbering formats that work
An invoice number only has two jobs: it must be unique, and it should be easy to find later. Most numbering systems are one of these:
| Format | Example | Good for |
|---|---|---|
| Sequential | INV-0001, INV-0002 | Almost everyone — simple and audit-friendly |
| Year + sequence | 2026-0042 | Seeing at a glance which year an invoice belongs to |
| Date-based | 20260512-01 | Businesses issuing several invoices a day |
| Client prefix | ACME-007 | Freelancers with a few regular clients |
| Project prefix | WEB24-03 | Agencies billing per project |
Use padding (0001 rather than 1) so invoices sort correctly in folders and spreadsheets. The tool above generates a batch of numbers with any prefix, starting number and padding you choose.
Invoice numbering rules to follow
- Never reuse a number, even for a cancelled invoice — issue a credit note instead.
- Don’t skip numbers without a record of why. In VAT/GST countries, tax authorities often expect a continuous sequence, and gaps can raise questions in an audit.
- Keep one sequence per business (or per series, if you deliberately run separate series for different branches or document types — e.g. CN- for credit notes).
- Don’t start at 0001 if you’d rather not look new — starting at 1001 is perfectly acceptable, as long as you continue sequentially.
- Put the number in the payment reference you ask clients to use, so you can match payments to invoices.
How the generator works
Enter a prefix (e.g. INV-), a starting number (e.g. 42), how many numbers you want, and the number of digits. With 4 digits and a count of 3, you’ll get INV-0042, INV-0043, INV-0044. Our main invoice generator also suggests the next number automatically each time you create an invoice, stored privately in your own browser.
Common questions
Do invoice numbers need to be sequential?
Not legally in most jurisdictions, but sequential numbering is standard practice and makes it obvious if an invoice is missing from your records.
Can I restart my numbering each year?
Yes — many businesses use a prefix like the year (INV-2026-0001) and reset the sequence annually. Just set your starting number and prefix accordingly here.
Do invoice numbers have to be sequential?
Many tax systems — particularly VAT and GST regimes — expect sequential, unique invoice numbers. Even where it isn’t strictly required, a sequential system makes record-keeping and audits much easier.
What number should my first invoice be?
Any number you like, such as 0001 or 1001, as long as every invoice after it follows in sequence without duplicates.
Can I have different numbering for different clients?
Yes, client or project prefixes are fine, but each full invoice number must still be unique across your business.
Turn this into a real invoice.
Use the full generator to build a proper, line-itemized invoice — free, no signup.