Table of Contents

1 Introduction

Calculation trees are relationships between concepts in a taxonomy that describe and validate simple totals and subtotals. An example of a calculation relationship is:

Gross Profit = Revenue – Cost of Sales

Calculation relationships help users of the taxonomy understand how concepts relate to other concepts in the taxonomy. They act as a guide for preparers in tag selection. XBRL validation software will flag an inconsistency if the fact values in a report do not add up according to the calculation relationships defined in the taxonomy. Thus, XBRL calculations are a valuable tool for defining concept semantics and checking the consistency of reports.

The Calculations 1.1 specification, finalised in February 2023, provides an incremental improvement on XBRL's existing calculation functionality. This document recommends the adoption path for the transition to Calculations 1.1 and is targeted towards taxonomy authors, data collectors, software vendors and preparers.

2 Calculations 1.1

The two key improvements of Calculations 1.1 are better handling of rounded numbers and duplicate facts.

2.1 Rounding

Company financial reports often present numbers in thousands or millions, and the presented numbers may not add up exactly due to rounding. XBRL's existing calculation functionality (now referred to as "Calculations 1.0") did not take the reported accuracy of facts into account when checking calculations, resulting in warnings being raised due to rounding, as discussed in this blog post on rounding errors.

Calculations 1.1 addresses this issue and does not flag warnings due to rounding. The resulting reduction in false warnings will be a welcome outcome for all stakeholders, including preparers, auditors, data collectors and users.

2.2 Duplicate Facts

Financial reports often include the same value multiple times in different sections of the report. Inline XBRL best practice is to tag all such occurrences of the fact in order to ensure consistency and to allow users to navigate between these different occurrences. Tagging of all occurrences of facts results in duplicate facts in an XBRL report.

Calculations 1.0 excluded calculation checks for duplicate facts, which means calculation inconsistencies may go undetected. Calculations 1.1 takes a new approach to handling duplicate facts, which ensures that calculations involving such facts are checked for consistency. This addition is critical to support the growing adoption of Inline XBRL in filing systems.

3 Calculations 1.1 Scope

Calculations 1.1 does not address all issues related to calculations in XBRL reports. Notably, Calculations 1.1 may still trigger false positives when there are incomplete fact sets. This occurs when there are enough facts to trigger a calculation, but not enough to check it completely. Preparers and other users should review all calculation inconsistencies, in order to determine whether further action is needed.

Calculations 1.1 will not detect all calculation inconsistencies if the calculation tree is incomplete.

Like Calculations 1.0, Calculations 1.1 only supports calculations between different concepts. It does not support cross-dimensional or cross-period calculations.

4 Adopting Calculations 1.1

Users are encouraged to migrate to Calculations 1.1 as soon as reasonably possible in order to benefit from the enhanced calculation consistency checking capability. XBRL tools will have to be updated to support the new standard.

XBRL validating processors will automatically use the improved calculation consistency check when a taxonomy uses the new Calculations 1.1 relationship type ("arcrole"):

https://xbrl.org/2023/arcrole/summation-item

The straightforward path for transitioning to Calculations 1.1 is to update the calculation tree in a taxonomy to use the new relationship type. This requires that all tools have been updated to adopt the new specification, so it may not always be practical to make this switch immediately.

The specification also allows tools to optionally use the improved Calculations 1.1 behaviour when using taxonomies that use the Calculations 1.0 relationship type. This ability will enable users to get the benefits of Calculations 1.1 when checking reports using existing taxonomies. This approach is intended as a migration path (and for checking historical filings), and it is recommended that taxonomies adopt the new relationship type in order to ensure that the newer behaviour is applied consistently.

Here is the recommended adoption path for different stakeholders for the transition to Calculations 1.1:

4.1 Taxonomy Authors

• Plan to adopt the Calculations 1.1 relationship type in upcoming taxonomy releases.
• The new relationship type is a replacement for the old one. Existing calculation relationships should be removed.

4.2 Data Collectors

• For reporting programmes allowing or requiring extension taxonomies, plan to update filing rules to require the use of the Calculations 1.1 relationship type in extension taxonomies.
• Encourage preparers to check XBRL reports using the new Calculation 1.1 behaviour as soon as their tools support it.
• Whilst preparers are to be encouraged to check calculations inconsistencies as part of their review process, it should not be made a requirement to submit reports with no calculation inconsistencies (at least in open reporting environments). There may still be a possibility of false positive calculation inconsistencies due to incomplete sets of facts.

4.3 Software Vendors

• Start implementing Calculations 1.1 in products.
• Provide an option to validate XBRL reports using Calculations 1.1 for taxonomies using the Calculations 1.0 relationship type.
• Clearly distinguish validation results based on the calculation consistency method used.

4.4 Preparers

• Extension taxonomies will need to start using the new Calculations 1.1 relationship type once required by filing rules (this should be handled automatically by preparation software).
• Start using Calculations 1.1 features when reviewing reports as soon as your tools support it, even if the taxonomy is using Calculations 1.0 relationships, because Calculations 1.1 results are less likely to include false warnings and may also flag new errors due to duplicate facts needing resolution.

5 Technical notes

5.1 Rounding Methods

Calculations 1.1 supports two rounding methods: 'round to nearest' and 'truncation'. 'Round to nearest' rounds to the closest digit. For example, 3.4 rounds down to 3 and 3.7 rounds up to 4¹. Truncation simply removes the digits to be rounded; 3.4 and 3.7 are both truncated to 3.

When checking calculation consistency using Calculations 1.1, users may have to select the rounding method used by the processor. This needs to match the method used in the report. Preparers need to ensure the same rounding method is used throughout the report. Rounding methods used by entities are typically based on the common practice for the reporting environment. In most cases, end-user software may default to an appropriate rounding mode for the region or filing system.

5.2 OIM Compatibility

Calculations 1.1 is built on top of the XBRL Open Information Model (OIM), which provides a simplified, syntax-independent model of XBRL Reports.

In order to achieve a simplified model, some less commonly used complex features are not supported by the XBRL Open Information Model. These include:

• Reports containing tuples;
• Concepts using a fraction data type; and
• Various dimensional features, including complex typed dimensions, non-dimensional segment/scenario content and mixing segment and scenario container elements.

Calculations 1.1 can only be applied to XBRL reports that conform to XBRL Open Information Model (OIM) constraints. An exception to this rule is that Calculations 1.1 permits reports to contain tuples, but calculation consistency checking will not be applied to facts within the tuples.