# BR-29 Invoicing period end must not precede its start

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

## Problem Description

> **ERROR**: EN 16931 core business rule (CEN)

## Context and Significance

This is an EN 16931 core rule and a value check. The invoicing period (BG-14) tells the buyer which period was delivered or billed, for example for subscriptions or maintenance contracts. An end date before the start date usually comes from swapped fields, a date read as MM/DD instead of DD/MM during conversion, or a typo in the year. The line-level counterpart is BR-30.

## Solution

Correct the dates in cac:InvoicePeriod (CII: ram:BillingSpecifiedPeriod/ram:StartDateTime and ram:EndDateTime) so the end date is on or after the start date, or remove the period if it was entered in error.

- [Validate XML](/en/xrechnung-validator?source=resource&rule=BR-29)
- [Convert invoice](/en/pdf-to-xrechnung?source=resource&rule=BR-29)

## Valid Examples

- BT-73 = 2026-01-01, BT-74 = 2026-01-31

## Invalid Examples

- BT-73 = 2026-01-31, BT-74 = 2026-01-01 — end before start

## Code Examples

### Valid XML
```
<cac:InvoicePeriod>
  <cbc:StartDate>2026-01-01</cbc:StartDate>
  <cbc:EndDate>2026-01-31</cbc:EndDate>
</cac:InvoicePeriod>
```

### Invalid XML
```
<cac:InvoicePeriod>
  <cbc:StartDate>2026-01-31</cbc:StartDate>
  <cbc:EndDate>2026-01-01</cbc:EndDate>
</cac:InvoicePeriod>
```

## Affected Fields

- [BT-73 Invoicing period start date](/resources/xrechnung/bt-73-invoicing-period-start-date)
- [BT-74 Invoicing period end date](/resources/xrechnung/bt-74-invoicing-period-end-date)

## Related Rules

- [BR-30](/resources/kosit-validator-errors/br-30-line-period-end-after-start)

## Validation Tools

- [Official KoSIT Validator](https://github.com/itplr-kosit/validator): Run the official KoSIT validator with the XRechnung configuration to check EN 16931 and XRechnung rules.
- [Convert PDF to XRechnung](/pdf-to-xrechnung): Find validation errors during conversion and review each correction.

## Related Resources

- [Official Specification](https://docs.peppol.eu/poacc/billing/3.0/rules/ubl-tc434/)
- [Test Suite](https://github.com/itplr-kosit/xrechnung-testsuite)
- [All validation errors](/resources/kosit-validator-errors): Overview of the EN 16931, XRechnung and Peppol validation rules explained here.