#Invoice ID

The Invoice ID is automatically generated by Simple Invoices when you save an invoice. It is made up of three parts combined together:

[Biller Prefix] + [Preference Prefix] + [Auto-incrementing Number]

#How It Works

#1. Biller Invoice Prefix

Set on each Biller under Settings → Billers → edit → Invoice Prefix.

This is an optional prefix that identifies which office, branch, or entity issued the invoice.

Examples: B1-, NY-, CA-, or leave blank for no prefix.

#2. Invoice Preference Prefix

Set on each Invoice Preference under Settings → Invoice Preferences → edit → Invoice ID Prefix.

This prefix typically indicates the document type or category.

Examples: INV- for invoices, QTE- for quotes, REC- for receipts.

#3. Auto-incrementing Number

A sequential counter managed in the si_index table. Each time an invoice is saved, the counter for that invoice's numbering group is incremented.

The number can be formatted using PHP sprintf format codes:

• %06d → 6-digit zero-padded (000042)
• %08d → 8-digit zero-padded (00000042)
• %04d → 4-digit zero-padded (0042)
• Leave empty → no padding (42)

#Full ID Examples

#Numbering Groups

See Invoice Numbering Groups for a detailed explanation of how preferences can share or separate their auto-increment counters.

#Where to Configure

#Important Notes

• The Invoice ID shown on the new invoice form is a preview only. The actual number is committed when you click Save.
• If multiple users create invoices simultaneously, the final ID may differ from the preview.
• After changing prefixes or formats on an existing preference, existing invoices are NOT retroactively updated. Use Settings → Invoice List Cache → Rebuild normalised fields to update them.
• The Invoice ID is separate from the database id column: it is the index_id field and is what appears on printed/emailed invoices.