# BR-DEC-02: Write the document allowance base amount with no more than two decimals

The `cbc:BaseAmount` of a document-level allowance has more than two digits after the decimal point. Write the base of the percentage discount with two.

- Layer: EN 16931
- Severity: fatal (the document is invalid)
- Topics: Allowances and charges
- Official definition: https://docs.peppol.eu/poacc/billing/3.0/rules/ubl-tc434/BR-DEC-02/
- Explanation last updated: 2026-09-28

## The short answer

`BR-DEC-02` fails when a document-level allowance, a `cac:AllowanceCharge` under the root with `cbc:ChargeIndicator` of `false`, gives its `cbc:BaseAmount` with more than two characters after the decimal point. Write the base amount of the discount with two decimals at most: `50.00`, not `50.000`.

The base amount is the figure a percentage discount is taken from, so it only appears beside `cbc:MultiplierFactorNumeric`. The recorded base of `50.000` for a 2 percent discount has the right value and one padding zero, and `UBL-DT-01` reports the same `cbc:BaseAmount` beside this rule.

## What the rule checks

The rule visits each allowance directly under the `Invoice` or `CreditNote` root, takes the text of its `cbc:BaseAmount` and counts the characters after the first full stop; three or more fail. A discount given as a fixed sum carries no base amount, so there is nothing to count and it passes.

Only the form of the base is tested, not whether it produces the allowance. When tried, a base of `50.004` reported this rule and `UBL-DT-01` alone: 2 percent of it is 1.00008, which `PEPPOL-EN16931-R040` accepts against the allowance of 1.00 because it allows 0.02 either way.

The indicator decides which rule counts a base amount. On a document charge, with `cbc:ChargeIndicator` of `true`, it belongs to `BR-DEC-06`; the gross price inside `cac:Price` is left alone by both rules and by `UBL-DT-01`. When tried, a price allowance of `1.000` on a gross price of `6.000` validated cleanly.

Fewer decimals are always fine. When tried, the base written as the whole number `50` validated.

| Term | Meaning | UBL element |
|---|---|---|
| BT-93 | Document level allowance base amount | `cac:AllowanceCharge[cbc:ChargeIndicator = false]/cbc:BaseAmount` |

## How an integration ends up here

Possible causes, from the shape of the rule rather than from measured usage:

- The base is the subtotal the discount applies to, added up from line amounts kept at three or four decimals and written without rounding.
- The allowance amount is rounded before it is written, but the base it came from is copied straight from the pricing engine.
- A decimal column with a scale of three stores 50 as 50.000, and the serialiser writes the full scale.

## How to fix it

1. Round the base amount to two decimals where the discount is calculated, then apply the percentage to the rounded base.
2. Write it to `cbc:BaseAmount` in the document-level `cac:AllowanceCharge` with at most two decimals and no whitespace.
3. Round the allowance `cbc:Amount` to two decimals as well, and keep it within 0.02 of base times percentage over 100 so that `PEPPOL-EN16931-R040` still agrees.
4. If the discount is really a fixed sum, leave out both the base amount and the percentage rather than rounding a base nobody needs.

## Before and after

These are fragments, not complete documents. The complete synthetic documents they come from are linked below.

Fragment of the failing invoice: a 2 percent document discount whose base is written as 50.000

```xml
<cac:AllowanceCharge>
  <cbc:ChargeIndicator>false</cbc:ChargeIndicator>
  <cbc:AllowanceChargeReasonCode>95</cbc:AllowanceChargeReasonCode>
  <cbc:AllowanceChargeReason>Example document discount</cbc:AllowanceChargeReason>
  <cbc:MultiplierFactorNumeric>2</cbc:MultiplierFactorNumeric>
  <cbc:Amount currencyID="GBP">1.00</cbc:Amount>
  <cbc:BaseAmount currencyID="GBP">50.000</cbc:BaseAmount>
  <!-- tax category omitted from this fragment -->
</cac:AllowanceCharge>
```

Fragment of the corrected invoice: the same base written as 50.00

```xml
<cac:AllowanceCharge>
  <cbc:ChargeIndicator>false</cbc:ChargeIndicator>
  <cbc:AllowanceChargeReasonCode>95</cbc:AllowanceChargeReasonCode>
  <cbc:AllowanceChargeReason>Example document discount</cbc:AllowanceChargeReason>
  <cbc:MultiplierFactorNumeric>2</cbc:MultiplierFactorNumeric>
  <cbc:Amount currencyID="GBP">1.00</cbc:Amount>
  <cbc:BaseAmount currencyID="GBP">50.00</cbc:BaseAmount>
  <!-- tax category omitted from this fragment -->
</cac:AllowanceCharge>
```

The failing and corrected invoices differ in one element, the base amount of the document discount: `50.000` against `50.00`. Both state the discount as 2 percent of that base, giving the allowance of 1.00 that the totals already use. The failing document reports `BR-DEC-02` at the first `cac:AllowanceCharge` and `UBL-DT-01` at its `cbc:BaseAmount`. `UBL-DT-01` applies two decimals to every element named as an amount, `cbc:BaseAmount` included, and exempts only the item net price and the amounts of a price-level allowance, so an allowance base that breaks this rule breaks that one as well. The corrected invoice is the larger example with its discount restated as a percentage, and it validates with no findings.

### What the validator reported

- The failing invoice reports **BR-DEC-02** and [UBL-DT-01](https://ironfang.com/docs/finance/rules/UBL-DT-01.md). The corrected document passes every layer with no findings.
  - [Download the failing XML](https://ironfang.com/finance/rule-examples/BR-DEC-02-invalid.xml)
  - [Download the corrected XML](https://ironfang.com/finance/rule-examples/decimals-allowance-percent-valid.xml)

Recorded on phive 12.1.0 / phive-rules-peppol 4.5.6 / Saxon-HE 12.10, the engine behind the free validator, using synthetic data. A recorded result is regression evidence for these documents; it is not a certification.

## Where it applies

- Applies to UBL `Invoice` and `CreditNote`. When tried, a credit note with the same 2 percent document discount on a base of `50.000` reported the same two findings.
- The limit is two decimals in every currency; `currencyID` is not read.
- Peppol ties the base amount to the percentage: `PEPPOL-EN16931-R041` requires a base when a percentage is given, and `PEPPOL-EN16931-R042` requires a percentage when a base is given. In a document that passes Peppol, then, a base amount appears only on a percentage allowance.

## Related rules

- [UBL-DT-01 reports the allowance base amount in the same run, as part of its limit on every amount element](https://ironfang.com/docs/finance/rules/UBL-DT-01.md)
- [PEPPOL-EN16931-R040 checks the allowance amount against this base and the percentage](https://ironfang.com/docs/finance/rules/PEPPOL-EN16931-R040.md)
- [BR-DEC-01 limits the amount of the same document allowance to two decimals](https://ironfang.com/docs/finance/rules/BR-DEC-01.md)
- [BR-DEC-06 is the matching limit for the base amount of a document charge](https://ironfang.com/docs/finance/rules/BR-DEC-06.md)

## Scope and source

Written for Peppol BIS Billing 3.0.21 (May 2026), EN 16931 1.3.16, as applied to UBL 2.1 Invoice and CreditNote documents. Other profiles, syntaxes and releases can define this identifier differently. Guidance version 2026-09-28.1: source checked 2026-09-28, explanation last updated 2026-09-28.

[The official definition of BR-DEC-02](https://docs.peppol.eu/poacc/billing/3.0/rules/ubl-tc434/BR-DEC-02/) carries the normative wording and test. This page is our explanation of it, not a copy.

Guidance does not change the engine verdict. Fixing this finding does not mean the document passes every layer, and validation does not certify legal or tax compliance or transmit a document over Peppol.

## Links

- [This rule as a web page](https://ironfang.com/docs/finance/rules/BR-DEC-02)
- [Free Peppol invoice validator](https://ironfang.com/tools/peppol-validator)
- [Rule index](https://ironfang.com/docs/finance/rules.md)
- [Ironfang Finance API docs](https://ironfang.com/docs/finance)
- The same rule is available to MCP clients as the tool `finance.rule.get` on https://mcp.ironfang.com/mcp