How to Number Invoices
Invoice numbers should be unique, traceable and ideally sequential. Common schemes are year-sequence (2026-0001) or client-initial-sequence. Never reuse a number; keep a voided invoice's number and mark it void instead of deleting it and leaving a gap.
Numbering rules
One sequence per entity; separate companies or currencies.
A year or month prefix helps filing, but do not reset to 1 each year and create duplicates.
Keep voided numbers and mark them void or link a credit note.
Recordkeeping
Keep invoices, payment records, credit notes and contracts.
Retention depends on local tax law; in the US it is often at least 3-7 years.
Export PDF/CSV backups instead of relying on one system.
FAQ
Must numbers be sequential?
Many tax/audit contexts require traceability; sequential is easiest, and gaps should be explainable.
Can I reuse a voided number?
No; it breaks the audit trail.