InvoiceCrispThree formats that work
Whatever you choose, numbers must be unique and should only go up. Leading zeros (0001) keep files sorted correctly.
- Sequential: INV-0001, INV-0002, INV-0003. The simplest, and fine for most small businesses.
- Date-based: 2026-10-001, 2026-10-002. Shows when an invoice was issued at a glance; restart the counter each month or year.
- Client-based: ACME-001, ACME-002. Handy when you bill a few large clients repeatedly.
Your first invoice number
You do not have to start at 1. Many freelancers start at 1001 or 0100 so a new client does not see "invoice #1". That is perfectly fine, as long as you keep counting up from there.
Mistakes and cancelled invoices
- Do not reuse or delete a number once you have sent the invoice.
- If an invoice was wrong, send a corrected one with a new number and note which invoice it replaces, or issue a credit note.
- Keep a list or spreadsheet of every number with its date, client and status, or let your invoicing tool do it.
Numbers for estimates and receipts
Use separate prefixes so documents never collide: EST-0001 for estimates, Q-0001 for quotes, INV-0001 for invoices and RCT-0001 for receipts. In the generator above, the prefix changes with the document type.
Frequently asked questions
Is invoice numbering required by law in the US?
There is no single federal rule, but the IRS expects you to keep records that support your income, and unique numbers make that much easier. Many countries, especially in the EU, do require sequential numbering.
Can InvoiceCrisp number invoices automatically?
Yes, with Pro: each new invoice takes the next number for its document type. On the free plan you type the number yourself.
Is InvoiceCrisp really free?
Yes. You can create and download unlimited invoices, estimates and receipts for free, with no sign-up. The free version uses the Classic template and adds a small "Created with InvoiceCrisp" line at the bottom. Pro removes it and adds more templates, saved clients and history.