# BR-CO-19 Invoicing period needs a start or end date

If the invoicing period (BG-14) is used, the invoicing period start date (BT-73) or the invoicing period end date (BT-74) shall be filled, or both.

## Problem Description

If the invoicing period (BG-14) is used, the invoicing period start date (BT-73) or the invoicing period end date (BT-74) shall be filled, or both.

> **ERROR**: XRechnung 3.0

## Context and Significance

This EN16931 core rule prevents an empty invoicing period group that would carry no billing timeframe information.

## Solution

When a cac:InvoicePeriod is present, provide at least a StartDate (BT-73) or an EndDate (BT-74); remove the period if neither applies.

- validate
- convert

## Valid Examples

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

## Invalid Examples

- cac:InvoicePeriod present but neither BT-73 nor BT-74 filled

## 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:DescriptionCode>3</cbc:DescriptionCode>
</cac:InvoicePeriod>
```

## Affected Fields

- [BG-14 Invoicing period](/resources/xrechnung)
- [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-CO-20](/resources/kosit-validator-errors/br-co-20-line-period-date-required)

## Validation Tools

- [Official KoSIT Validator](https://erechnungsvalidator.service-bw.de/): Validate your XRechnung files against all BR-DE rules.
- [Convert PDF to XRechnung](/pdf-to-xrechnung): Automatic validation error fixes when converting.

## Related Resources

- [Official Specification](https://xeinkauf.de/xrechnung/)
- [Test Suite](https://github.com/itplr-kosit/xrechnung-testsuite)
- [Complete Error List](/resources/kosit-validator-errors): Overview of all German XRechnung validation rules.