# BT-73 Invoicing period start date

Start date of the period to which the invoice applies.

## Quick answer

> **Delivery and payment**: Delivery dates, payment means, and the operational context around settlement.

- [Validate XML](/en/xrechnung-validator?source=resource&bt=BT-73)
- [Convert invoice](/en/pdf-to-xrechnung?source=resource&bt=BT-73)

## In plain language

Start date of the period to which the invoice applies.

Start date of the period to which the invoice applies.

Important for subscriptions, rentals, and all invoices that bill a service period instead of a single delivery moment.

## What you usually enter here

ISO 8601 date format (YYYY-MM-DD)

Typical valid values include: 2026-04-01, 2026-01-01

Optional according to EN 16931-1.

## What goes wrong often

Avoid values like: 01.04.2026, 2026/04/01

## Examples in context

Important for subscriptions, rentals, and all invoices that bill a service period instead of a single delivery moment.

Optional according to EN 16931-1.

## Valid Examples

- 2026-04-01
- 2026-01-01

## Invalid Examples

- 01.04.2026
- 2026/04/01

## Related Fields

Important for subscriptions, rentals, and all invoices that bill a service period instead of a single delivery moment.

- [BT-74 Invoicing period end date](/resources/xrechnung/bt-74-invoicing-period-end-date)
- [BT-72 Actual delivery date](/resources/xrechnung/bt-72-actual-delivery-date)

## 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-73

### Data Type:
date

### Cardinality:
0..1

### Requirement:
Optional

### Since Version:
Optional

## XML Implementation

### UBL 2.1 Syntax
```
/Invoice/cac:InvoicePeriod/cbc:StartDate
```

### CII (UN/CEFACT) Syntax
```
/CrossIndustryInvoice/SupplyChainTradeTransaction/ApplicableHeaderTradeDelivery/ram:BillingSpecifiedPeriod/ram:StartDateTime
```

## Create an XRechnung from your PDF

The converter reads the invoice and shows the fields it found before download, so you can check and correct the values. No PDF? Fill in the XRechnung directly in the form.

- [Convert invoice](/en/pdf-to-xrechnung)
- [Fill in XRechnung in the form](/en/create-xrechnung)

Download requires an account. Subscriptions from €10/month with annual billing (excl. taxes), or €5 per conversion (excl. taxes) without a subscription.

## Why the standard cares about this field

### Business Context
Important for subscriptions, rentals, and all invoices that bill a service period instead of a single delivery moment.

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

## Official sources and tools

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