# HR-BR-51

Source: https://xmlvalid.com/rules/HR-BR-51

> Početni datum obračunskog razdoblja stavke računa (BT-134) mora biti veći od 01.01.1900. i manji od 01.01.2100.

- Level: error
- Rule sets: Croatian eRačun rules (UBL) 13.03.2026
- Context: `cac:InvoiceLine | cac:CreditNoteLine`
- Test: `((xs:date(cac:InvoicePeriod/cbc:StartDate) >= xs:date('1900-01-01')) and (xs:date(cac:InvoicePeriod/cbc:StartDate) < xs:date('2100-01-01'))) or (not(exists(cac:InvoicePeriod/cbc:StartDate)))`

In English: The invoice line period start date (BT-134) must be after 1 January 1900 and before 1 January 2100.

Validate a document against these rules: https://xmlvalid.com/validate