# BR-29

Source: https://xmlvalid.com/rules/BR-29

> If both Invoicing period start date (BT-73) and Invoicing period end date (BT-74) are given then the Invoicing period end date (BT-74) shall be later or equal to the Invoicing period start date (BT-73).

- Level: error
- Rule sets: EN 16931 rules (UBL) 1.3.17, EN 16931 rules 1.3.16 (UBL), EXTENDED-CTC-FR rules (UBL) 1.4.0.04, Romanian RO e-Factura rules (UBL) 1.0.9
- Context: `cac:InvoicePeriod`
- Test: `(exists(cbc:EndDate) and exists(cbc:StartDate) and xs:date(cbc:EndDate) >= xs:date(cbc:StartDate)) or not(exists(cbc:StartDate)) or not(exists(cbc:EndDate))`

> If both Invoicing period start date (BT-73) and Invoicing period end date (BT-74) are given then the Invoicing period end date (BT-74) shall be later or equal to the Invoicing period start date (BT-73).

- Level: error
- Rule sets: EN 16931 rules (CII) 1.3.17, EN 16931 rules 1.3.16 (CII), EXTENDED-CTC-FR rules (CII) 1.4.0.04, Factur-X BASIC WL rules 1.09, Factur-X EN 16931 rules 1.09.2, Factur-X EXTENDED rules 1.09.2
- Context: `//ram:ApplicableHeaderTradeSettlement/ram:BillingSpecifiedPeriod`
- Test: `(ram:EndDateTime/udt:DateTimeString[@format = '102']) >= (ram:StartDateTime/udt:DateTimeString[@format = '102']) or not (ram:EndDateTime) or not (ram:StartDateTime)`

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