# BT-26 Preceding invoice issue date

Issue date of the preceding invoice referenced in BT-25.

## Quick answer

Issue date of the preceding invoice referenced in BT-25.

> **Invoice basics**: Core document identifiers, dates, process identifiers, and high-level invoice context.

## In plain language

Issue date of the preceding invoice referenced in BT-25.

Issue date of the preceding invoice referenced in BT-25.

The date helps recipients identify the exact earlier invoice when invoice numbers alone are not enough.

## What you usually enter here

ISO 8601 date format (YYYY-MM-DD)

Typical valid values include: 2026-03-15

Optional according to EN 16931-1.

## What goes wrong often

Avoid values like: 15.03.2026

## Examples in context

The date helps recipients identify the exact earlier invoice when invoice numbers alone are not enough.

Optional according to EN 16931-1.

## Valid Examples

- 2026-03-15

## Invalid Examples

- 15.03.2026

## Related Fields

The date helps recipients identify the exact earlier invoice when invoice numbers alone are not enough.

- [BT-25 Preceding invoice reference](/resources/xrechnung/bt-25-preceding-invoice-reference)

## XML mapping and field facts

Open the technical reference if you need XML paths, validator rule codes, legal wording, or schema-specific mapping details.

### Field ID:
BT-26

### Data Type:
date

### Cardinality:
0..1

### Requirement:
Optional

### Since Version:
Optional

## XML Implementation

### UBL 2.1 Syntax
```
/Invoice/cac:BillingReference/cac:InvoiceDocumentReference/cbc:IssueDate
```

### CII (UN/CEFACT) Syntax
```
/CrossIndustryInvoice/SupplyChainTradeTransaction/ApplicableHeaderTradeSettlement/ram:InvoiceReferencedDocument/ram:FormattedIssueDateTime
```

## Why the standard cares about this field

### Business Context
The date helps recipients identify the exact earlier invoice when invoice numbers alone are not enough.

### Legal Requirement
Optional according to EN 16931-1.

## Official sources and tools

- [KoSIT Validator](https://erechnungsvalidator.service-bw.de/)
- [Invoice Converter](/pdf-to-xrechnung)
- [XRechnung Standard](https://xeinkauf.de/xrechnung/)
- [Test Suite](https://github.com/itplr-kosit/xrechnung-testsuite)