Invoice numbering

With Lago, invoice numbers are automatically generated each time an invoice is finalized. You can configure how these numbers increment to match your billing entity structure and customer management needs.

Per customer: Generates a unique invoice sequence for each customer. This method ensures isolated and traceable numbering per customer, which can simplify customer-level reporting and accounting.
Entity-wide numbering: Uses a single, continuous sequence across all customers within a billing entity. The invoice number also carries the year and the month (YYYYMM), so you can segment invoices by period. The sequence itself does not restart each month.

Invoice prefix customization

Lago also allows full control over the prefix applied to documents like invoices and credit notes. By default, the prefix combines:

The first three letters of your billing entity’s name, and
The last four characters of your entity ID.

Both are uppercased, so a billing entity named “Acme Corporation” gets a prefix such as ACM-9F3C. You can override this with a custom prefix of 1 to 10 characters to match your internal conventions.

Examples

For a billing entity whose prefix is ACM-9F3C, an invoice finalized in January 2026 is numbered:

Setting	Invoice number	Reading
Per customer	`ACM-9F3C-005-003`	third invoice of the customer whose sequence is `005`
Entity-wide	`ACM-9F3C-202601-001`	first invoice of the billing entity, finalized in January 2026

A draft invoice has no sequential number yet. It is shown as ACM-9F3C-DRAFT until you finalize it.

Configure numbering through the API

Set document_numbering to per_customer or per_billing_entity, and document_number_prefix to the prefix you want:

LAGO_URL="https://api.getlago.com"
API_KEY="__YOUR_API_KEY__"
BILLING_ENTITY_CODE="acme_corp"

curl --location --request PUT "$LAGO_URL/api/v1/billing_entities/$BILLING_ENTITY_CODE" \
  --header "Authorization: Bearer $API_KEY" \
  --header 'Content-Type: application/json' \
  --data-raw '{
    "billing_entity": {
      "document_numbering": "per_billing_entity",
      "document_number_prefix": "ACM"
    }
  }'

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Invoice numbering